PANACEA OR PLACEBO – A weekly series assessing the evidence behind complementary and alternative medicines.
Herbs have been used for therapeutic purposes in most cultures for hundreds and even thousands of years. The father of Western medicine, Hippocrates (460 BC – 377 BC) is known to have used many plants and herbs for medicinal purposes. Hippocrates' use of up to 400 plants are well documented in a collection called the Corpus Hippocraticum.
Western herbal medicines have traditionally been used to help prevent and treat diseases. Many useful pharmaceuticals have been derived from such herbs, including:
salicylic acid to make aspirin from the bark of the white willow tree (Salix alba);
morphine from the poppy plant (Papaver somniferum);
digitalin, digitoxin and digoxin from the plant foxglove (Digitalis purpurea);
atropine from the belladonna plant (Atropa belladonna) and;
quinine from the bark of the quinine tree (Cinchona ledgeriana).
In herbal medicine, the whole plant or parts of the plant (flowers, leaves, bark, fruit, seeds, stems and roots) are used for their potential therapeutic properties.
Herbal medicines differ from pharmaceuticals as they contain complex multi-component substances, and like pharmaceuticals can exert biochemical and physiological effects on the body. There are natural variations of the active components in herbs, which is why there are differences in the profiles of batches of the same herbal ingredient.
This variation creates difficulties for research and analysis of systematic reviews of trials. Standardisation of extracts of herbs has improved over the years but remains an ongoing issue for both research and clinical use.
Safety is also an issue for herbs. As they contain active substances, herbs can cause adverse reactions as a result of interacting with pharmaceutical drugs. A good example is St John’s wort, which is used for treating mild depression. The hyperforin levels found in this plant can result in reduced efficacy for drugs such as digoxin, the oral contraceptive pill and warfarin.
Western herbal medicines used by Hippocrates and still commonly used today include fennel, cinnamon, clove, chaste-berry, anise or licorice, coriander, garlic, St John’s wort, white willow bark, valerian, linseed, peppermint, chamomile, celery, clove (oil), Viscum album, elder-wood, sage and nettle.
The evidence base
Most of the evidence for herbal medicine stems from traditional use accumulated over hundreds of years and is documented in key monographs. Randomised control trials have also been conducted for some herbs but the majority vary in quality, lack methodological rigour, are often of short duration and have small numbers of participants.
Still, there are some Cochrane reviews and research worthy of mention that demonstrate the potential effectiveness of some herbs. Cranberry tablets (not the juice) for the prevention of recurrent urinary tract infections in young women, for instance, or St John’s wort for mild, moderate and major depression, various herbs (STW 5 and STW 5-II) for irritable bowel syndrome, and rosehip and avocado-soybean unsaponifiables for osteoarthritis.
As the trials included in the systematic reviews are quite diverse, it’s difficult in some cases to know the type of extract, dosage or form of herbs that are most active and clinically effective.
Larger rigorous and high-quality trials are needed to help identify which herbs or standardised extracts of herbs are clinically useful. This would also help identify the safety profile of Western herbal medicines, especially with prolonged use.
This is the sixth article in our series Panacea or Placebo. Click on the links below to read the other instalments: