Some of the best-known medicines come from poisonous plants. The chemotherapy drug taxol comes from the yew tree, morphine from the opium poppy and digoxin from the foxglove. These plants can have lethal toxicity if taken in their raw form. Digoxin is prescribed to treat angina at doses a thousand times more dilute than most prescription medications, highlighting the plant’s extreme potency.
Many people consider herbal medicines a safe alternative to pharmaceuticals. And it’s true that many herbal medicines are fairly mild. However, there is a less well-known group of herbal medicines that are far more potent and controlled under the Medicines Act, where they are restricted to use by medical herbalists and at strictly defined dosages.
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These are known as the schedule 20 herbs in the UK and are prescribed for a variety of health needs. All of these plants are toxic at relatively low doses, mainly due to the presence of chemical compounds called alkaloids, which also have healing properties.
Here are ten examples of these deadly, healing plants.
1. Wild saffron
Known as wild saffron or the autumn crocus, Colchicum autumnale is one of the oldest known medicinal plants. It was first mentioned in the Egyptian medical text, Ebers Papyrus (circa 1550BC), where it was described for the treatment of pain and swelling. It is still used in medicine, chiefly for its anti-inflammatory properties and particularly for the treatment of gouty arthritis.
2. Deadly nightshade
Atropa belladonna is commonly known as deadly nightshade. All parts of the plant are pain relieving, antispasmodic, hallucinogenic, narcotic and sedative. Containing tropane alkaloids (the same group as cocoaine), it is used predominantly for the gastrointestinal tract (colic, gastritis, IBS), but also for asthma and for urinary spasm, Parkinson’s disease and topically for pain relief.
Deadly nightshade has healing properties too. Greens and Blues/Shutterstock
3. Greater celandine
Greater celandine is often seen when walking in the woods. It has a long history of medical use in eastern and central European folk medicine to treat asthma, bronchitis, jaundice, digestive issues and even cancer. However, due to the presence of isoquinoline alkaloids, it has the potential to cause severe liver toxicity when ingested and many experts advise against its use. It can be used relatively safely as a poultice or cream to treat warts and verrucae.
Greater celandine is common in woodland. Zhanna Bohovin/Shutterstock
4. White quebracho
White quebracho is a tropical tree from South America. Rich in indole alkaloids, which are also present in psychoactive drug psilocybin, it has traditionally been used to treat fever, malaria, swellings, stomach upsets, cough, headaches, syphilis, impotence and asthma.
5. Fever tree
Species of chinchona or “fever tree” have been used worldwide to treat malaria. The drug quinine is extracted from its bark. It was introduced into Europe in the 17th century for the treatment of fevers. Although it is commonly used as an appetite stimulant, recent research has suggested that it may have a role to play in weight management and obesity too.
6. Thorn apple
Datura stramonium or thorn apple has traditionally been used for various ailments including respiratory conditions, ulcers, wounds, inflammation, rheumatism and gout, sciatica, bruises and swellings and fever. Modern research has shown that it may also have potential in the treatment of epilepsy.
Thorn apple may look fragile but it is a restricted drug. Roman Nerud/Shutterstock
7. Ephedra sinica
Ephedra sinica has been known in traditional Chinese medicine for approximately 5,000 years. The plant contains the alkaloids ephedrine and pseudoephedrine, some of the first drugs to be used in the treatment of respiratory conditions. Side effects can include psychosis, delusions and hallucinations, which is one of the reasons drugs obtained from this plant were restricted in the UK in 2014 for cough and cold remedies for use in young children. The psychoactive properties of ephedra also explain its notoriety as a recreational drug and a number of deaths in the US have been linked to its misuse.
8. Henbane
Plants in the nightshade family, including henbane, are potent medicinal plants. They are purported to have anti-diabetic, antioxidant, anticancer, insecticidal, antiasthmatic, antiallergic, antidiarrhoeal, cardioprotective, anticonvulsant and antidepressant effects but more research is needed. However they also contain psychoactive compounds that can cause delirium and hallucinations.
Henbane is no mild herb. mutie/Shutterstock
9. Pheasant’s eye
Adonis vernalis, (pheasant’s eye) leaves and flowers have long been used in European and east Asian folk medicine to treat cardiovascular conditions. Studies have shown the chemical constituents within this plant also have antimicrobial and anti-inflammatory effects. The cardiovascular effects are largely attributed to the cardiac glycosides (chemicals that slow down heart rate) contained within this plant, which are also responsible for its toxicity, in a similar way to the foxglove.
10. Lily of the valley
A common poisonous plant often found in the garden, lily of the valley, has historically been used to treat cardiovascular conditions such as arrythmias, heart failure and angina. Another plant that contains cardiac glycosides, its common presence in gardens is a particular danger for children and pets.
Other toxic healers
Not all toxic plants are on the schedule 20 list however. Garden herbs comfrey and borage contain pyrrolizidine alkaloids that can be toxic to the liver and comfrey has been banned for medicinal use in many European countries. Comfrey, also known as knitbone, is mainly used topically as an anti-inflammatory and analgesic for acute sprains and strains or more chronic conditions such as osteoarthritis.
Belonging to the same family, borage is not that well known as a medicinal herb in the UK, whereas in Mediterranean countries it has a strong reputation for treating a range of conditions. It is credited with sedative properties, useful for insomnia, and dizziness and melancholy. In gynaecology, it can shift postpartum exhaustion, and helps with the symptoms of menopause. The oil from this plant contains negligible amounts of these alkaloids and supplements are often processed to remove the toxicity.
In the UK there are several professional associations that hold a register of qualified medical herbalists. Learning the right dosage to give a patient was just as important for folk healers. Modern science may help us verify which plants are best for healing but getting the dosage right is an ancient skill.
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