REVIEW ARTICLE
Toxic treasures: A review of therapeutic compounds from
poisonous plants
T. Cherian
Former Faculty Member, Faculty of Medicine, United Arab Emirates University, UAE and Kuwait
University, Kuwait
Corresponding author: Dr. T. Cherian Email: tcvazhuvelil@gmail.com
Journal of Experimental Biology and Zoological Studies. 1(2): p 71-85, Jul-Dec 2025.
Received: 04/06/2025; Revised: 22/06/2025; Accepted: 25/06/2025; Published: 01/07/2025
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Abstract
Humans have historically harnessed the inherent toxicity of living organisms for diverse
applications, from hunting and warfare to traditional medicine. This ancient knowledge has
significantly contributed to the development of numerous modern pharmaceuticals derived
from natural compounds. While plants are essential for life, they also produce toxins as a
defense mechanism, which can be detrimental upon ingestion. Paradoxically, these very
compounds can offer therapeutic benefits when administered in controlled doses. The
perceived "safety" of a plant is, therefore, not absolute; it is contingent upon individual factors
such as sensitivity, genetic predisposition, health status, and hormonal balance. By integrating
scientific research with traditional knowledge, we can better understand this dual nature of
plant compounds, enabling us to both mitigate potential risks and leverage their benefits in
medicinal and other fields. This underscores the intricate chemistry of the natural world and
humanity's remarkable capacity for resilience and adaptation. This review further explores the
toxic constituents found in sixteen common plants and their current therapeutic applications in
modern medicine.
Keywords: Atropa, Digitalis, Curarea, odollam, Gloriosa, Ricinus, Nux-vomica, Cannabis, Opium,
Nicotiana, Abrus, Oleander, Aconitum, Datura, Catharanthus, Serpentine, Atropine, Scopolamine,
Hyoscyamine, Reserpine, Yohimbine.
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Introduction
The inherent capacity of living organisms to produce toxins has been historically leveraged by
ancient civilizations for diverse purposes, including hunting, tribal warfare, and traditional
medicine. Indeed, a significant number of modern pharmaceuticals have been developed based
on this ethno-medical knowledge and the applications of naturally occurring compounds.[1] The
production of toxins is a natural phenomenon observed across eukaryotes, encompassing both
plants and animals, often serving as a mechanism for defence and survival. A classic example
of this is Alexander Fleming's observation of a fungal metabolite produced by Penicillium
notatum that inhibited bacterial growth. This substance, which Fleming later named penicillin
revolutionized the treatment of bacterial diseases in 1941.[2] The development of modern drugs
and pharmacologically active compounds derived from plants used in traditional medicine has
been made possible through the collaborative efforts of scientists worldwide. Over the past 75
years of extensive research, modern medicine has isolated thousands of compounds and drugs
that are now used to treat a wide range of diseases.
Plants serve as the primary source of food and energy for living organisms, providing essential
nutrients, vitamins, and vital elements crucial for animal survival. However, as a defence
mechanism against herbivores, insects, and parasites, certain plant species produce toxic
substances that can exert adverse effects on humans and animals, if ingested. These plant toxins
are diverse chemical compounds concentrated in various plant parts including roots, stems,
leaves, flowers, and fruits. They present significant risks, ranging from mild gastrointestinal
disturbances to severe organ damage and even mortality.[3] Chronic exposure to certain plant
extracts, sometimes employed in traditional medicine, can also lead to cumulative toxicity and
the development of conditions such as liver cirrhosis or kidney failure.[4] Conversely, the
inherent toxicity of some plant compounds holds therapeutic and pharmacological significance
when administered in controlled dosages, finding applications in patient treatment and drug
discovery initiatives.[1] Common classes of toxic compounds present in plants include
alkaloids, glycosides, saponins, cyanogenic compounds, oxalates, phenolics, and flavonoids.
Understanding the dual role of these plants as both life-sustaining and potentially lethal,
highlights the importance of careful study and respect for the complex chemistry of the natural
world. Traditional knowledge of the effectiveness of toxic components, supported by animal
studies, in vitro experiments, and carefully controlled clinical trials, is now being used in
modern medicine to treat many diseases. Many modern drugs are of natural product origin and
about 50% of them play an important role in drug development programs in the pharmaceutical
industry. Even though some plants are known for their highly toxic components, certain plants
considered safe for consumption can still cause adverse effects in some individuals. This
phenomenon arises from the varying toxicity potential of plant substances, which can affect
people differently due to many reasons. These substances can trigger immune responses that
manifest as skin rashes, hives, swelling, or even anaphylaxis. Some fruits, nuts, and seeds
trigger very severe allergic reactions, sometimes life-threatening. Certain fruits can adversely
affect the body's physiology under the influence of elevated hormone levels and trigger
abnormal effects in a presumably normal physiological situation such as pregnancy.[4] In
essence, the "safety" of plant materials is not absolute but rather depends on the individual
consuming or coming into contact with it. Factors such as genetic predisposition, pre-existing
health conditions, the amount consumed, and even hormonal status can influence whether a
plant substance elicits a beneficial, neutral, or adverse reaction.
Some of the toxic plants which produce a diverse range of bioactive molecules making them
precious sources for diverse medicinal applications are mentioned below.
1. Atropa belladonna
Atropa belladonna, commonly known as deadly nightshade is a highly toxic perennial
herbaceous plant belonging to family Solanaceae. Usually a native to temperate southern,
central, and eastern Europe, North Africa, Turkey and Iran, this plant is also found in Simla
and Kashmir in India (Figure 1). It has been introduced and naturalized in some parts of
Canada and the United States. All parts of the plant are highly poisonous, containing potent
tropane alkaloids, including atropine, scopolamine, and hyoscyamine.[5]
Figure 1: Atropa belladonna
It is a shrub reaching up to 15 feet tall with dull green, oval-shaped leaves, bell-shaped, dull
purple flowers with green tinges and a faint scent (Figure 1). The fruits are glossy black berries,
about the size of cherries, which are sweet-tasting and particularly attractive to children, posing
a significant danger. The plant extract was used by early tribes as arrow poison for hunting and
tribal war, making it a lethal weapon. Despite its toxicity, Atropa belladonna has a long and
varied history of use. The name "bella donna" meaning "beautiful woman", the plant extract
was used by Italian women during renaissance time to dilate their pupils, considered a sign of
beauty.[6]
Ingestion, especially of the berries, can lead to severe anticholinergic poisoning. Symptoms of
poisoning can include tachycardia, dilated pupils, blurred vision, dry mouth, difficulty in
swallowing, high fever, flushed skin, agitation, delirium, hallucinations, inability to urinate or
sweat, spasms, mental confusion, convulsions, coma and death due to respiratory failure. It is
also toxic to domestic animals, potentially causing paralysis and death. The antidote for
belladonna poisoning is physostigmine or pilocarpine.[6,7]
The alkaloids atropine, scopolamine and hyoscyamine extracted from belladonna have
important medicinal properties.[7] Atropine is a medication that has a variety of effects on the
body due to its action as an anticholinergic agent. It primarily works by blocking the effects of
acetylcholine, a neurotransmitter. It can treat bradycardia by blocking the vagal nerve's
influence on the heart, thereby increasing the heart rate. In the eye, atropine dilates the pupils
and hence is useful for eye examinations and treating certain eye conditions. It can relax the
smooth muscles in the stomach, intestines, bladder, and other organs, which can help relieve
spasms. Atropine is a crucial antidote for poisoning caused by organophosphate pesticides and
nerve agents. These substances increase acetylcholine levels, and atropine blocks their effects
at muscarinic receptors. Scopolamine is used to reduce body secretions and stomach acid,
control heart rate, and relax muscles. It is also known for its use in treating motion sickness.
Scopolamine acts as a nonselective competitive antagonist at muscarinic acetylcholine
receptors. By blocking acetylcholine, it inhibits parasympathetic nervous system activity,
causing various effects. In the central nervous system, it particularly affects M1 receptors,
contributing to its antiemetic, sedative, and amnestic properties. Its action on the vestibular
system and the vomiting centre in the brainstem is key to preventing nausea and vomiting.
Peripherally, it primarily affects M3 receptors, reducing glandular secretions and relaxing
smooth muscles. Hyoscyamine is used to relieve gastrointestinal disorders, like irritable bowel
syndrome (IBS) and spasms.[8] It is an anticholinergic medication with effects similar to
atropine and scopolamine, as it blocks the action of acetylcholine in the body. Hyoscyamine
works by competitively inhibiting the action of acetylcholine at muscarinic receptors in smooth
muscle, secretory glands, and the central nervous system. This blockade leads to the relaxation
of smooth muscle, reduced secretion of various fluids, and can have central nervous system
effects, although generally less pronounced than scopolamine.[9]
Throughout history, belladonna has been used as a poison, both intentionally and accidentally.
Due to its high toxicity and unpredictable effects, self-medication with the plant is extremely
dangerous and should be avoided entirely. Any medicinal use should be done under strict
medical supervision with isolated and purified compounds. In conclusion, Atropa belladonna
is a plant with a captivating history, known for its poisonous properties and valuable medicinal
alkaloids.
2. Digitalis purpurea (Fox Gloves)
Digitalis purpurea is native to temperate Western and Central Europe and northwest Africa.
This plant is seen in India at the high altitudes of Jammu & Kashmir, Assam, West Bengal,
Kerala, Uttarakhand and Himachal Pradesh (Figure 2). Digitalis purpurea, commonly known
as foxglove is admired for the beauty of its flowers; typically, purple but pink, rose, yellow and
white colours are also seen. This plant is highly toxic but has valuable medicinal properties.
Foxglove has a long history in medicine for treating heart conditions. In 1775 William
Withering described its use for oedema from heart failure noting that extracts of the leaves
increased urine output and strengthened the pulse.[10] Later researchers found out that the plant
leaves, flowers and seeds contain potent cardiac glycosides, principally digitoxin and digoxin.
These glycosides inhibit the Na+/K+-ATPase pump in cardiac cells, leading to increased
intracellular sodium which, in turn, increases the calcium influx via the sodium-calcium
Figure 2: Digitalis purpurea
exchanger, strongly affecting heart function. The net effect is a stronger (positive inotropic)
heartbeat. Digoxin also stimulates the vagus nerve, slowing conduction through the AV node
and reducing heart rate (negative chronotropic effect).[11] Thus, digitalis drugs increase cardiac
contractility and help control ventricular rate in atrial fibrillation. In modern cardiology,
digoxin (brand name Lanoxin) is prescribed for selected patients with heart failure or atrial
fibrillation who continue to experience symptoms despite other medical therapy. Although
considered safe, digoxin has a narrow therapeutic window, and clinicians are taking utmost
care in treating patients to avoid its toxicity. [12,13]
3. Curarea toxicofera
Curarea toxicofera is a vigorous climbing vine growing up to 20 metres, found in the humid
rainforests of tropical America, mostly at low elevations (Figure 3). It is abundant in Amazon
rainforest and in countries like Colombia, Ecuador, Peru, Brazil, Venezuela, and Bolivia. This
plant is a well-known arrow poison used by indigenous people for hunting. The poisonous
substance is an alkaloid called curare present in the plant, particularly in the root. Curare acts
as a neuromuscular blocking agent.[14]
Figure 3: Curarea toxicofera
In an experimental frog nerve-muscle preparation, stimulation of the nerve can lead to the
release of neurotransmitters, primarily acetylcholine (ACh), which then binds to receptors on
the postsynaptic muscle, causing contraction. Curare blocks the action of ACh by binding to
the receptors, preventing muscle contraction. It binds to nicotinic acetylcholine receptors at the
neuromuscular junction causing muscle paralysis. This paralysis typically progresses in live
animals, eventually affecting the respiratory muscles, leading to death by respiratory arrest.
Importantly, curare is only toxic when it enters the bloodstream parenterally. It is not active
when ingested orally and hunters can safely consume animals killed with curare toxin.[14]
While historically known for its poisonous properties, tubocurarine also has uses in modern
medicine. Curare derivatives are primarily used as muscle relaxants, often administered
alongside general anaesthesia during surgeries, especially of the chest and abdomen, to achieve
profound muscle relaxation. They can be used to relax the throat muscles, making it easier to
insert a breathing tube. This effect of curare can be reversed using anticholinesterase drugs like
neostigmine.
4. Cerbera odollam (Othallam)
Cerebra odollam (local name Othallam) is a tree belonging to the family Apocynaceae that
include several poisonous species of plants (Figure 4). Its seeds are excessively toxic
containing a cardenolide called cerebrin. The odollam tree is responsible for about 50% of the
plant poisoning cases and 10% of the total poisoning cases in Kerala. There are numerous
instances in which it is misused for both suicide and homicide. Odollam tree grows to a height
of 50ft and has large white flowers with a faint smell of jasmine. While highly toxic, some
Figure 4: Cerebra odollam
research explores its potential medical uses. Studies suggest that the seeds have anticancer
properties through apoptotic activity. Fruit extracts exhibit enhanced anticancer properties
when used in combination with other treatments in certain cancer cell lines. Leaf extracts have
been screened for antioxidant properties. In traditional medicine the wood has been used in
paralysis treatment. The latex has been used as an emetic and purgative. The plant has been
investigated for use as a bio-insecticide, insect repellent, and rat poison. The potential use of
Cerbera odollam for medical applications are still under investigation. It is worth mentioning
that ingestion of any part of this plant, especially the seeds, is extremely dangerous and should
be avoided.[15]
5. Gloriosa superb (Flame Lily)
Gloriosa superba, also known as Flame Lily is native of Africa, China and Asia including the
Indian subcontinent (Figure 5) and has been used in traditional Ayurvedic medicine for many
diseases. This is a poisonous plant due to the presence of alkaloids like colchicine and
gloriosine. Discovered more than 3,000 years ago, colchicine is one of the oldest drugs still in
use today. It was mentioned in the oldest Egyptian medical text, Ebers Papyrus (1550 B.C.),
where it was described for relieving pain and treating swellings. In traditional medicine it has
been used in small doses for gout and rheumatism, bruises, sprains, arthritic pain, skin
problems, ulcers, colic and indigestion, leprosy, piles, fever, and as a general tonic.[16]
Figure 5: Gloriosa superba
Ingestion of any of its parts can lead to severe symptoms, including nausea, vomiting,
diarrhoea, burning sensation, numbness, and potentially life-threatening complications like
respiratory depression, cardiovascular issues, and multi-organ failure. The toxic alkaloid,
colchicine, interferes with cell division. In modern medicine colchicine is used primarily for
the treatment of gout, an inflammation in a joint.[17] Colchicine does not cure gout, but it
prevents gout attacks. Colchicine is also used to reduce the risk of heart attack, stroke, certain
types of heart procedures, and cardiovascular death in patients with atherosclerosis or with
multiple cardiovascular risk factors. However, it is a potent drug with a narrow therapeutic
window and used under strict medical supervision.[18]
6. Ricinus Communis (Castor Oil Plant, Avanaku)
Ricinus communis (Avanaku), the castor oil plant, belonging to the family Euphorbiaceae, has
a history of various medicinal applications, primarily through its oil (castor oil) extracted from
its seeds (Figure 6). It has naturalized throughout tropical and subtropical regions worldwide.
It can also be found in some temperate countries, where it is being cultivated. Castor oil is well-
known for its potent laxative properties. It contains ricinoleic acid which interact with the
prostanoid receptors on the intestinal smooth muscle causing influx of calcium causing
contraction. By the same mechanism it can cause uterine smooth muscle contraction,
suggesting its potential usage in the induction of labour.[19] Topical application of castor oil has
been used for dry skin warts, fungal infections, inflammation and joint pains.[20]
Figure 6: Ricinus communis
While castor oil itself is generally considered safe for its intended uses, the seeds are highly
toxic as it contains ricin, a potent toxin. Ingestion of the seeds can cause severe poisoning, with
symptoms including nausea, vomiting, abdominal pain, and in severe cases, dehydration, organ
damage, and even death. The primary medicinal usage of this plant is through castor oil, mainly
as a laxative and for some topical applications.[20]
7. Strychnos nux-vomica (Kanjiram)
Strychnos nux-vomica is a deciduous tree native to India and south east Asia. It is a medium-
sized tree coming under the family Loganiaceae that grows in open habitats (Figure 7). It is
known for being the natural source of the extremely poisonous alkaloids strychnine and brucine
which affect the nervous system.[21] It has a long history of use in traditional medicine systems
like Ayurveda, Unani, and Traditional Chinese Medicine. Its usage in modern medicine is very
limited and highly cautious due to its potent toxicity.[22]
Figure 7: Strychnos nux-vomica
Strychnine poisoning can lead to muscle spasms, convulsions, respiratory failure, and
death. Experiments are going on to find out the effects of various compounds isolated from
this tree for anti-inflammatory, antioxidant, and even anticancer effects.[23] However, these are
preliminary findings and far from clinical applications due to the toxicity concerns. Nux
vomica is a well-known remedy in homeopathy, used for a wide range of conditions,
particularly digestive issues, irritability, and hangovers. However, it's important to note that
homeopathic preparations use highly diluted substances. Due to its toxicity, the use of
Strychnos nux-vomica parts and strychnine is heavily regulated in many countries. It is a well-
known rodenticide and known for killing stray pests. Strychnos nux-vomica is not used in
modern allopathic medicine due to its high toxicity. While traditional systems value it in
carefully processed forms and minute doses, modern medicine generally relies on safer and
more effective alternatives.[23]
8. Cannabis sativa
Cannabis (Figure 8) is a genus of flowering plants in the family Cannabaceae that is widely
accepted as an intoxicating plant grown in Indian subcontinent and has been in use since 1000
BCE. Cannabis sativa, has gained significant attention for its modern medicinal uses. This is
largely attributed to its diverse chemical compounds, collectively known as cannabinoids, with
the most well-known being tetrahydrocannabinol (THC) and cannabidiol (CBD).[24]
Cannabis sativa, including varieties like indica can be toxic, particularly in high doses or for
certain individuals. While not typically fatal, cannabis intoxication can cause temporary
adverse effects like anxiety, confusion, respiratory distress, and gastrointestinal problems.
Chronic use can lead to more serious issues like cannabinoid hyperemesis characterized by
nausea, vomiting, and abdominal pain and potential cardiovascular effects. Overconsumption
of cannabis can lead to symptoms like difficulty in coordinating movements, decreased muscle
strength, lethargy, and delayed responses. In some cases, higher doses can cause confusion,
amnesia, delusions, or hallucinations.[24]
Figure 8: Cannabis sativa
Cannabis and cannabinoids may be effective in relieving chronic pain, particularly neuropathic
pain. Certain cannabinoid medications, dronabinol and nabilone, which are synthetic forms of
THC are approved to treat nausea and vomiting caused by chemotherapy.[25] Oral cannabinoids
may help improve spasticity symptoms in some people with multiple sclerosis. CBD-based
medications like epidiolex are approved for treating specific severe forms of epilepsy.
Dronabinol is also approved for medical use to stimulate appetite in individuals with AIDS-
related weight loss. Cannabinoids might play a role in treating sleep issues. There is some
evidence suggesting cannabis may help relieve symptoms of post-traumatic stress disorder. It
also has analgesic, antiemetic and appetite-stimulating properties. A non-psychoactive
cannabinoid such as CBD has shown potential therapeutic effects, with anti-inflammatory,
analgesic, anti-anxiety, and anti-seizure properties.[26]
9. Papaver somniferum (Opium poppy)
Papaver somniferum, commonly known as the opium poppy (Family Papaveraceae) is an
annual flowering herb growing to about 40 inches (Figure 9). Originally a native of eastern
Mediterranean regions, it was propagated throughout the world by different rulers, traders and
races. Opium poppy is an incredibly significant plant and historically been used from the third
century B.C. for the treatment of dysenteries. The term opioid refers to all compounds related
to opium. It is used in modern medicine as it contains numerous alkaloids such as morphine,
codeine, thebaine, papaverine and noscapine that are classified as narcotic drugs. Their use is
strictly regulated due to the risk of abuse and dependency.[27] Australia, Turkey and India are
the major producers of poppy for medicinal purposes and poppy-based drugs, such as morphine
or codeine.
Morphine is a highly effective narcotic analgesic commonly used to manage severe pain,
including post-surgical pain, cancer-related pain, and pain associated with heart attacks. It can
be administered orally, intravenously, or epidurally. Codeine is a mild analgesic and
antitussive, commonly used to treat mild to moderate pain. It is included in some cough syrups
to suppress coughing. Thebaine is not directly used as an analgesic; it is a precursor in the
synthesis of other opioids like oxycodone, a semi-synthetic opioid analgesic used for moderate
to severe pain and naloxone which is an opioid antagonist. Hydrocodone is another semi-
synthetic opioid analgesic, often combined with other pain relievers like acetaminophen.
Papaverine is primarily used as a vasodilator, to relax smooth muscles and improve blood flow.
It has applications in treating erectile dysfunction and some vascular conditions. Noscapine
has been studied for its potential anticancer and antitussive properties, although it is not as
widely used as morphine or codeine. Morphine and thebaine extracted from Papaver
somniferum are chemically modified to produce other important opioid medications, including
heroin, diacetylmorphine. While having potent analgesic effects, its high addictive potential
restricts its medical use in many countries.[25]
Figure 9: Papaver somniferum
In summary, Papaver somniferum is fundamental to modern medicine as the natural source of
vital opioid analgesics like morphine and codeine, as well as precursors for other synthetic and
semi-synthetic opioids used to manage pain and other conditions. The cultivation and
processing of opium poppies for medicinal purposes are strictly regulated globally due to the
addictive nature of these substances.[28]
10. Nicotiana tabacum
Nicotiana tabacum (tobacco) is a toxic plant which, belongs to the family Solanaceae (Figure
10). Historically and in some traditional medicine systems, tobacco has been used for various
medicinal purposes. Native Americans traditionally used it for conditions like bronchitis,
toothache, healing wounds and skin issues. Traditional Chinese Medicine also documented its
use for pain relief and detoxification. Tobacco is mainly used in cigarettes and other tobacco
products. The plant contains an alkaloid called nicotine which gives a sense of pleasure through
its effects on the brain. Smoking of tobacco is an addiction as nicotine stimulates the brain to
release dopamine, a neurotransmitter associated with pleasure and relaxation. Nicotine, along
with other alkaloids like anabasine, acts on nicotinic receptors, causing various physiological
effects that can be toxic. Nicotine is a highly toxic alkaloid and it acts on nicotinic acetylcholine
receptors, causing a chain of events that can lead to various toxic effects. Nicotine's action on
nicotinic receptors leads to increased sodium ion influx, membrane depolarization, and
enhanced action potential propagation. This affects the central and autonomic nervous systems,
neuromuscular junctions, and the adrenal medulla, leading to a range of symptoms. Exposure
to nicotine can cause symptoms like abdominal pain, hypertension, tachycardia, tremors, and
even respiratory failure in severe cases. Poisoning can occur through ingestion, skin contact,
or occupational exposure.[29]
Nicotiana tabacum and its components are used in modern medicine for Nicotine Replacement
Therapy (NRT). It is available as patches, gums, lozenges, inhalers and nasal sprays. It contains
various other phytochemicals. Much emphasis is placed in modern medical and pharmaceutical
research on these metabolites, excluding the harmful components of smoke, to elucidate their
Figure 10: Nicotiana tabacum
potential therapeutic value in neurodegenerative diseases such as Alzheimer’s and Parkinson’s,
inflammatory conditions like colitis, arthritis, and multiple sclerosis, as well as metabolic
disorders including obesity and fatty liver.[30] However, this research is still in its early stages,
and many of these components have yet to be fully explored or integrated into mainstream
medical practice as anticipated.
11. Abrus precatorius (Kunnikuru)
While Abrus precatorius (Kunnikuru) has a long history of use in traditional medicine, its usage
in modern medicine is extremely limited due to its high toxicity (Figure 11). The seeds contain
abrin, a potent toxin that can be fatal if ingested, especially if the seeds are chewed or broken.
In traditional systems of medicine like Ayurveda, after careful detoxification processes, various
parts of Abrus precatorius have been used for premature greying and hair fall. Paste made
from purified seeds is used for joint pain, swelling, and sciatica; root powder mixed with honey
is used for cough; leaf decoction for cough and flu; and leaf paste for leucoderma and other
skin conditions. Seed powder is used for treating worms. The plant also holds significance in
traditional medicine, where it is used as an aphrodisiac, abortifacient, and in the treatment of
jaundice and snakebites. Due to the potent toxicity of abrin, Abrus precatorius is not generally
used in mainstream modern medicine. The risks associated with its internal use without proper
Figure 11: Abrus precatorius
detoxification are very high. However, there is some modern research exploring the potential
of certain compounds found in Abrus precatorius. Studies are underway on the potential use
of seed extracts in protecting against oxidative damage in the eye lens, antimicrobial, anti-
diabetic, anti-tumor, and anti-inflammatory properties.[31] Researches are investigating the
potential use of the plant with various extracts of the plant parts.
12. Nerium oleander (Arali)
Nerium oleander popularly known as ‘oleander’ or ‘arali’ is an ornamental plant coming under
the family Apocynaceae. It is grown in gardens for its beautiful pink, red, yellow and white
flowers (Figure 12). The plant is widely seen in the tropical and subtropical regions and is
commonly recognized as a toxic plant to animals. Toxicity in humans is rarely reported.
Animal deaths are common as they may eat the leaves and flowers of this plant in large quantity,
which causes acute poisoning. Many incidents of deaths of domestic animals due to eating
oleander flowers and leaves have been reported in Kerala. It has been shown in animal studies
that the toxicity of oleandrin is about 40-50mg/kg body weight.[32] That means a person of 60
kg body weight needs at least 3 grams of toxin to show an effect. It is known that oleander
leaves are more poisonous than the flowers and has been estimated that 12-15 oleander leaves
can produce a fatal quantity of the toxin in the human blood.
Figure 12: Nerium oleander
The toxin oleandrin can cause both gastrointestinal and cardiac effect. The central nervous
system manifestations of oleandrin toxicity are confusion, dizziness, drowsiness, weakness,
visual disturbances and mydriasis. The most serious side effects of oleander poisoning are
cardiac abnormalities, including various ventricular dysrhythmias, tachyarrhythmias,
bradycardia, and heart block. The poison oleandrin can produce burning sensation in oral
cavity, headache, vomiting, gastric colic, hyperkalaemia and diarrhoea. It can cause cardiac
arrhythmias possibly through electrolyte imbalances by disturbing the homeostasis mechanism
of the body. Even if the toxicity is not dangerous, prolonged vomiting and diarrhoea can cause
the loss of electrolytes leading to death if no proper medical attention is given. In traditional
medicines, oleander parts have been used and tried for its presumed therapeutic purposes.
Nevertheless, there is no clinical evidence that oleander or its constituents, including oleandrin,
are safe or effective in any disease.[33] During Covid-19 pandemic, the Trump administration
in US was considering oleandrin as a phytochemical to treat the disease; however, it was not
approved by FDA. Oleander plant tissues contain cardenolide glycosides, a phytotoxin, that
are capable of exerting positive inotropic (force of contraction) and negative chronotropic
effects (decreased heart rate) on the heart muscles of animals and humans. Pharmacological
action of oleander cardenolides is similar to that of the classic digitalis glycosides by inhibiting
Na+ K+ ATPase enzyme but there are differences in toxicity and extra cardiac effects. Toxic
exposures of humans and wildlife to oleander cardenolides occur throughout geographic
regions where these plants are grown. The human mortality associated with oleander ingestion
is generally very low, even in cases of intentional consumption. Experimental animal models
have been successfully utilized to evaluate various treatment protocols designed to manage
toxic oleander exposures.[34]
13. Aconitum heterophyllum
Aconitum heterophyllum is a perennial herb native to the Western Himalayas, found in Jammu
& Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, Nepal and Pakistan (figure 13). It
typically grows at high altitudes in the sub-alpine and alpine zones, ranging from 2500 to 4000
metres above sea level. It prefers grassy slopes in the alpine Himalayan region and sometimes
grows in forests with humus-rich soils. Aconitum contains diterpenoid alkaloids, including
benzoyecasonine, mesaconitine, aconitine, hypaconitine, heteratisine, atidine, isotisine,
hetidine, and hetsinone. Aconitine, found in many Aconitum species, is a highly toxic
cardiotoxin and neurotoxin. Symptoms of Aconitum poisoning generally include neurological,
cardiovascular, and gastrointestinal issues.[35] However, some reports suggest that Aconitum
heterophyllum may not contain or have very low levels of aconitine compared to other
Aconitum species. But it does contain other intensely bitter alkaloids. Traditional preparation
methods, such as boiling and purification, are employed to reduce potential toxicity. [36]
Figure 13: Aconitum heterophyllum
Aconitum heterophyllum has significant use in traditional medicine systems like Ayurveda and
Chinese Medicine. It is used to reduce fever, especially in paediatric medicine, indigestion,
flatulence, abdominal pain, and diarrhoea. It is also used in alternative medicine as an
expectorant for treating coughs, bronchitis, and asthma.[36] It is used to relieve pain and
inflammation. Anthelmintic, antiemetic, hepatoprotective, antioxidant, and
immunomodulatory effects also have been reported. Modern research is exploring its
antimicrobial, anti-inflammatory, analgesic, antioxidant, and nephroprotective activities.
14. Datura stramonium (Thorn Apple, Ummum)
Datura stramonium is an annual, erect, herbaceous plant that typically grows to a height of 0.5
to 1.5 meters (Figure 14). It is believed to be native to Central America but has naturalized
widely throughout the world in temperate and tropical regions. It thrives in disturbed sites, such
as wastelands, roadsides, cultivated fields, and gardens. It prefers rich, well-drained soil and
sunny locations. In India, including Kerala, it can be found as a common weed, particularly in
wastelands and along roadsides. It tends to flourish during the warmer months.[8]
All parts of Datura stramonium are highly toxic. The concentration of toxic alkaloids can vary
depending on the plant's age and the specific part. The primary toxic compounds are tropane
alkaloids, including scopolamine (hyoscine), hyoscyamine, atropine.[37] These alkaloids have
anticholinergic effects, blocking the action of acetylcholine in the central and peripheral
nervous systems. Symptoms of Datura poisoning can appear rapidly and may include, dilated
pupils (mydriasis), blurred vision, dry mouth and skin, rapid heartbeat (tachycardia), increased
body temperature, flushed face, restlessness, agitation, confusion, hallucinations, delirium,
seizures and coma. Accidental poisoning can happen through ingestion of seeds or other plant
parts. There are also documented cases of intentional misuse for hallucinogenic effects, which
is extremely dangerous due to the unpredictable and severe toxicity.[38]
Figure 14: Datura stramonium
Historically, Datura stramonium has been used in traditional medicine in various cultures. But
due to its high toxicity, its use in modern medicine is very limited and highly controlled.
Traditional practices include smoking the leaves to relieve symptoms of asthma and topical
application for pain and muscle spasms. The isolated tropane alkaloids, scopolamine,
hyoscyamine, atropine are used in modern pharmacology allowing for precise dosing and safer
application. Scopolamine is used to prevent motion sickness and sometimes as a pre-
anaesthetic to reduce secretions. Atropine is used as a mydriatic, to treat bradycardia, and as
an antidote for certain types of poisoning. Hyoscyamine is used to treat gastrointestinal
disorders such as irritable bowel syndrome.[37]
15. Catharanthus roseus
Catharanthus roseus is formerly known as Vinca rosea is widely cultivated as an ornamental
plant in almost all tropical and subtropical countries worldwide (Figure 15). It has been grown
as a garden plant for its colourful flowers. All parts of Catharanthus roseus are considered
poisonous if consumed orally by humans and animals. The toxicity is due to the presence of
various alkaloids, including vincristine and vinblastine. If ingested it can produce stomach
cramps, nausea and vomiting, and diarrhoea as immediate sign of poisoning. It also produces
hypotension, cardiac complications, and neuropathy and in severe cases systemic paralysis
leading to death.[39]
Figure 15: Catharanthus roseus
Despite its toxicity, Catharanthus roseus is a significant medicinal plant, primarily known as
a source of vinca alkaloids used in cancer chemotherapy. The plant contains alkaloids like
vincristine, vinblastine, vinflunine, and vindesine, which are used to treat various cancers,
including leukaemia, Hodgkin’s lymphoma, breast cancer, lung cancer, neuroblastoma Wilms'
tumour, testicular carcinoma and urothelial carcinoma.[40]
16. Rauvolfia serpentina (Local name Sarpagandha)
Rauvolfia serpentina belonging to the family Apocynaceae is a native of Indian subcontinent
and Southeast Asia usually well adapted to hot and humid climates (Figure 16). Rauvolfia
serpentina contains several alkaloids, including ajmaline, ajmalicine, reserpine, and serpentine
and yohimbine, which are potent toxins and can cause side effects.[41] In folk medicine, it has
been used for snake and insect bites, fever, malaria, abdominal pain, dysentery, and to stimulate
uterine contractions during childbirth. The plant was mentioned in Hindu manuscripts as long
ago as 1000 BC.
Figure 16: Rauvolfia serpentina
The alkaloid reserpine lowers blood pressure by depleting neurotransmitters in the sympathetic
nervous system, leading to vasodilation and a reduced heart rate. In the past, it was widely used
to treat hypertension.[42] Traditionally, it has been used to manage anxiety, insomnia, and
psychosis. Although reserpine has sedative and tranquilizing effects, its use for severe mental
disorders has largely been replaced by safer alternatives. Ajmaline is effective as an
antiarrhythmic, particularly in treating Brugada syndrome and acute atrial or ventricular
tachycardia. Ajmalicine is also used in the management of circulatory disorders and possesses
potential neuroprotective and anti-inflammatory effects. Serpentine exhibits antihistaminic
activity and has been used in traditional medicine for treating snakebites, along with its known
anti-inflammatory properties. Yohimbine, an α2-adrenergic receptor antagonist, works by
blocking the action of norepinephrine at the receptor level. It has been explored in various
research contexts, particularly for its effects on cardiovascular and neurological functions.[43]
Conclusion
In conclusion, the term "poisonous" when applied to plants is fundamentally a relative concept,
contingent upon dosage, individual sensitivity, and the specific context of human interaction.
Far from being inherently malicious, the compounds we perceive as toxic are, in fact, vital
biochemical tools that have evolved over millennia to serve crucial roles in the plant’s survival
acting as deterrents against herbivores, defences against pathogens, or even as facilitators in
reproductive strategies. Toxic plants and their therapeutic use underscore that the plant-derived
substances are not arbitrary threats but rather sophisticated products of natural selection,
integral to the ecological balance and a need for the plant’s survival. As intelligent beings,
humans have consistently demonstrated a remarkable ability to adapt, learn, and innovate, often
transforming adversity into opportunity. Through the integration of scientific research,
traditional knowledge, and technological advancement, the complexities of plant biochemistry
can be progressively unravelled. This growing understanding enables us not only to mitigate
the potential dangers of certain plant compounds but also to harness their benefits for
medicinal, agricultural, and industrial applications. In doing so, we move beyond a simplistic
notion of “toxins” towards a more nuanced appreciation of nature’s intricate chemistry and our
own adaptive ingenuity.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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