Medicines Derived From Plants
Aspirin and the Willow Tree
There can be very few of us who haven’t taken aspirin at some point in our lives to treat a cold, headache, toothache or other pain. More recently its blood thinning properties were recognised when trials showed that a low daily dose of aspirin can reduce the chance of strokes and heart attacks significantly. My only memory of taking an aspirin is that I was promptly sick and whilst that could have been unrelated I’ve stuck with paracetamol ever since.
Bark from willow trees (Salix family) contains a lot of salicylates and it is from these that aspirin (acetylsalicylate) was developed. The first person to formally recognise the medical properties of willow bark was Edmund Stone an English clergyman. In a letter written in 1763 he described how powdered willow bark could be used to treat fevers (New Scientist, Gareth Morgan, February 2004).
Indigestion, feeling sick or being sick are relatively common side effects of aspirin, but millions of people take it daily with no reported side effects. Uncommonly, but worth noting it can cause and allergic reaction which may need immediate treatment.
Digitalis and the Foxglove
Digitalis, in the form of the drug digoxin is commonly used to control heart conditions such as heart failure and an irregular or rapid heartbeat. In the case of heart failure, digoxin can help the heart to pump blood more effectively which should lead to an improvement of the patient’s symptoms. The symptoms include shortness of breath and oedema. The most common side effects of digoxin include dizziness, particularly when you first stand up and blurry vision.
The value of digitalis was recognised by William Withering in 1775 (Great Discoveries in Medicine, Bynum 2011). He was both a botanist and a medical doctor. Having heard that an old herbalist was successfully treating oedema in patients using a tincture she made herself, he experimented and discovered that the active ingredient came from the leaves of the foxglove (Digitalis purpurea).
Since an estimate 30% of all deaths are caused by heart disease (WHO Cardiovascular Diseases Fact sheet No 317), digoxin looks likely to remain a much used and valued drug.
Morphine and Poppies
Opium or laudanum from opium poppies (Papaver somniferus) has been used for hundreds of years to sooth pain. It was even given to Victorian babies who kept their mother’s awake with teething pain and a lot of it was consumed in fens of East Anglia to give pain relief to malaria victims (New Scientist. Fred Pearce. December 2001). Malaria was still common in the fens at that time because the malaria mosquito thrived in the marshland.
Morphine is an alkaloid of opium and is still obtained from the juice of opium poppy seeds. Afghanistan is a well-known producer of opium. More surprisingly in the 19th century, the village of Mitchum in southern England was renowned for producing opium.
Side effects include feeling or being sick in the first few days of taking it, drowsiness and a reduced breathing rate, called respiratory depression. Morphine dependence can occur if it is taken regularly for a long time. However, if your Doctor is prescribing you morphine they will have determined that the risk of this is outweighed by the potential benefits of the drug.
Periwinkle and Vinca Alkaloids
Gabrielle Hatfield (New Scientist 14th Oct 1995) found early 18th-century records of a treatment for breast cancer being a poultice of periwinkle plants (species of Vinca). Vinca major was a common garden plant in the UK then and is frequently planted today. 200 years later researchers discover that the Madagascar periwinkle contains alkaloids which can treat cancers such as leukaemia, lymphoma and multiple myeloma. They have developed the anti-cancer drug vincristine from the periwinkle. This is used in chemotherapy via infusion through a drip into patients’ veins. Common side effects are constipation, stomach pain and numb hands and feet.
Scientist know that many rainforest plants are rich in alkaloids which protect them from disease and insect attacks so there are certain to be more medical drugs derived from them in the future.
Quinine and Cinchona Trees
The genus of Cinchona trees has arguably proved to be one of the most important plant families in human medicine. There are 23 species in the group all from the South American Andes. The powdered bark from many of them, which we now know contains the active ingredient Quinine, has been treating Europeans suffering from malaria since the 17th century. Native South Americans were undoubtedly using in long before that.
Malaria in humans is caused by five species of Plasmodium parasites (one is very rare in humans). It is transmitted from human (host) to human via the bite of infected female anopheles mosquitoes (vector). In humans this causes severe fever, headaches and sickness and can cause death by disrupting the blood supply to vital organs.
Plasmodium Life Cycle - Causing Malaria
In 2010, more then 72,000 deaths from malaria occurred in Africa, mostly among children under five years of age. This amounts to 90% of all malaria deaths worldwide (World Health Organisation).
In the 1820s scientists were able to actually extract the quinine from the bark and began to work out which species of Cinchona produced the most quinine. One species which proved to be quinine rich was Cinchona. ledgeriana. Around 1865 To make money from Chinchona plantations, the Dutch successfully introduced to C. ledgeriana to the island of Java where it still grows today (Kew.org, A Short History of Cinchona).
In the 17th century malaria was prevalent through much of Europe and was also a hindrance when it came to exploring ‘distant lands’ such as South America and Africa, so quinine was widely used then. With an estimated 20% mortality rate from malaria (New Scientist, Tegan Dolstra, Nov 2010), treatment with quinine would have been welcomed and potentially life saving. Unfortunately the malaria parasite develops resistance to treatment and now even the most modern drug is less effective at treating some cases. With an estimated 655000 deaths from malaria in 2010 (World Health Organisation Malaria fact sheet No 94), Plasmodium is still a big killer.
According to the British Medical Journal, quinine has recently been shown to be effective for treating leg cramps. Some of the most common side effects of quinine are ringing in the ears (tinnitus), headaches and blurred vision. However it is much more dangerous if you take too much. Between 1969 and 2006, 93 deaths in America were linked to quinine and American doctors have been advised in general not to prescribe quinine for leg cramps (Boots WebMD).
Taxol and Yew Tree
Another anti-cancer drug which has been derived from a plant is Taxol from the bark of the Pacific yew tree (Taxus brevifolia). Marketed as paclitaxel, it has been used to treat ovarian and breast cancer and AIDS related Kaposi’s sarcoma. Because it can cause an allergic reaction steroids and antihistamine drugs are given to a patient before a paclitaxel drip to help reduce some of the side effects (Cancer Research UK). Common side effects include numb or tingling digits, achy joints and muscles and a rash.
Historical Use of Plants in Medicine
Before modern medicine and the manufacture of synthetic drugs, plants had been in use as medication probably as long as humans have existed. There are even reports of chimpanzees using leaves to self-medicate. Researchers in Africa have noticed chimps swallowing whole the leaves of certain Aspilia species. Usually they chew leaves before swallowing them. The same plants are used by local people to treat stomach disorders such as intestinal worms. Analysis of the leaf shows that it contains a powerful anthelmintic chemical (New Scientist, Cathy Sears, Aug 1990). Although it’s hard to prove conclusively that the chimps are aware of what they are doing, extensive observations indicate that that they do associate the leaves with relief from stomach pain.
Many people are still happy to refer themselves to a herbalist to cure or help manage their conditions and in Chinese medicine herbalists are held in as much esteem as doctors. As with mainstream medicines that come from plants, the danger is assuming that because it’s natural it won’t be harmful. This is not true of course. Many poisons come from plants and traditional remedies involving plants may not have undergone the rigorous testing that occurs with scientifically proven medicines.
With the caveat that you should not make use of any of the following plants for medical purposes without seeking further advice, here are a few of the plants, with their listed historical medical use, which Kew Gardens have in the medical section of their ‘Economic Botany Collection’.
- Lesser Celendine (Ranunculus ficaria) – used for digestive system disorders and piles.
- Compass plant (Silphium laciniatum) – used to induce vomiting (an emetic) and for digestive system disorders.
- Wormwood (Artemisia brevifolia) – used as an anthelmintic to treat intestinal worms.
- Indian heliotrope (Heliotropium indicum) – used as a dressing for insect bites and boils.
- Viriginian pokeweed (Phytolacca Americana) – used as a remedy for rheumatism.
- Flowering almond (Prunus japonica) – used to treat rheumatism and diseases of the genitourinary system.