HERBAL remedies are more popular than ever. Estimates vary, but the global
market has grown rapidly in the past decade, and according to the European
Herbal Practitioners Association, the European Union market is worth E6.8
billion a year.
No one doubts that herbs are full of medicinal chemicals鈥攁fter all,
plants are the source of half the pharmaceuticals in our modern medicine
cabinet. Most of the top seven sellers seem to have something going for them.
But why take a risk by swallowing something as
unpredictable as plant material when modern science can isolate the active
ingredient and serve it to you straight?
Herbalists claim it is because mixtures are better than pure chemicals. They
say the dozens of biologically active compounds in a plant work together to
produce a greater effect than any one chemical on its own. It sounds like New
Age hokum. But scientists are finding that the herbalists are sometimes
right.
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In fact, herbs could point us towards a whole new generation of drugs. Modern
medicine is hooked on the idea of the 鈥渕agic bullet鈥濃�攖he pure drug
molecule, like aspirin or penicillin. Even multi-drug approaches such as
combination therapy for HIV are just more of the same. Each ingredient in the
cocktail is a magic bullet in its own right.
Revolutionary though modern medicine has been, there are a host of illnesses,
from depression to multiple sclerosis, for which there is no magic bullet. Some
respond better to the kind of mixtures found in herbs. Is it time for a
rethink?
The first hints that herbalists were onto something came in the early 1990s,
when Raphael Mechoulam, head of pharmacology at the Hebrew University in
Jerusalem, discovered human receptors that bind tetrahydrocannabinol or THC, the
main active ingredient in cannabis.
Although the function of these receptors remains obscure, Mechoulam also
discovered that we make our own signalling molecules that bind to them. One,
2-AG, is produced alongside two companion compounds. Though closely related to
2-AG, neither has a biological effect on its own. But they do enhance the
potency of 2-AG by making it bind to its receptor more strongly. In other words,
the chemicals act in synergy鈥攖he mixture has an effect greater than the
sum of its parts.
鈥淚 have no idea how they do that,鈥� admits Mechoulam. But he suspects similar
chemical partnerships explain why whole herbs can work better than their single
purified ingredients. Hundreds of MS sufferers who use cannabis as a remedy
swear the whole plant works better than pure THC. Could it be that other
chemicals in cannabis work like 2-AG鈥檚 companions, enhancing THC鈥檚 affinity for
cannabinoid receptors?
There is certainly evidence that cannabis taken whole works better than
isolated extracts. At a symposium at the Royal Pharmaceutical Society in London
in April, pharmacologist Elizabeth Williamson of the University of London School
of Pharmacy reported that in a mouse model of MS, an extract of whole cannabis
relieved muscle spasms much more effectively than pure THC. Williamson says this
shows chemicals other than THC enhance the effect, but not whether the action of
these is synergistic or merely additive.
Some herbal derivatives seem to show true synergy. Hildebert Wagner and
colleagues at the University of Munich have shown that a mixture of two
anti-clotting chemicals found in ginkgo leaves is more powerful than the sum of
their individual effects. Similarly, the six most active chemicals in the herbal
sedative kava kava seem to act synergistically.
Williamson says additive or synergistic effects may make for better therapies
because you can achieve the medicinal effect with smaller doses of each
ingredient. That means you can avoid the side effects that tend to kick in with
higher doses. There鈥檚 anecdotal evidence that this is true: the herbal stimulant
ephedra, for example, is said to have fewer side effects than ephedrine, one of
its ingredients.
But no one has done any research to find out why. The mainstream
pharmaceuticals industry isn鈥檛 really interested in herbs because they鈥檙e
unpatentable. To market herbal derivatives with full patent protection, they
would have to do clinical trials on the active ingredients, separately and
together. Compared with testing a single magic bullet, this is prohibitively
expensive.
And there is a downside to these complex interactions. The better brands of
the herbal antidepressant St John鈥檚 Wort, for example, contain specific
quantities of one of the active ingredients, hypericin. But since there are a
dozen or more active compounds in the herb, two batches with the same hypericin
content might have very different potencies.
In any case, most herbal preparations are marketed with little testing, even
to make sure they contain the plants they claim to. European manufacturers try
to ensure that at least the safety, if not the efficacy, of their products is
tested, but they are under pressure from the US industry to weaken even these
controls. Without the support of the pharmaceuticals industry, herbs are likely
to remain mired in uncertainty. What a waste.
Garlic
Garlic bulb in oil or powder form. Traditionally used in the Far East as an
antiseptic. Now used to treat high cholesterol and elevated blood pressure.
Active ingredient unknown. Can cause indigestion and nausea. Harmful drug
interactions are rare, but can cause excessive thinning of the blood if taken
with warfarin (for general information on herb-drug interactions, see
http://www.mayohealth.org/ home?id=SA00039).
The evidence is mixed. An analysis of 13 trials found that garlic was better
than placebo for lowering cholesterol, but that the effect was modest
(Annals of Internal Medicine, vol 133, p 420). A review of 8 trials
concluded it was of 鈥渟ome clinical use鈥� for mild cases of high blood pressure,
but recommended more rigorous trials (Journal of Hypertension, vol 12,
p 463).
Ginseng
A root extract from any one of several different plants, usually Korean
ginseng (Panax ginseng) or American ginseng (Panax
quinquefolius). Used as a general tonic, it is said to increase resistance
to stress, combat ageing, improve immune function and boost physical and sexual
performance. The active ingredients are unknown. Can cause diarrhoea and high
blood pressure. Some harmful drug interactions.
Research is hindered by the fact that numerous plants go by the name of
ginseng. A recent analysis of 16 trials concludes that its effectiveness is not
established, but its popularity 鈥渨arrants more rigorous investigations鈥� (
European Journal of Clinical Pharmacology, vol 55, p 567).
Kava Kava
The rhizome of the South Pacific pepper plant Piper methysticum.
Historically taken as a narcotic drink, it鈥檚 now used as a sedative. The active
ingredients, kavapyrones, have been isolated and have a similar effect to
tranquillisers. Can cause mood changes, blurred vision, loss of muscle
coordination and, in large doses, hepatitis. Some harmful drug interactions.
There鈥檚 little doubt that kava kava works. A recent review of 7 trials
concluded that it was better than placebo and was 鈥渨arranted as a treatment
option for anxiety鈥� (Journal of Clinical Psychopharmacology, vol 20, p
84).
Echinacea
The roots and leaves of two North American plants, Echinacea
purpurea and Echinacea augustifolia. Used by native Americans to
treat wounds, burns, snake bites and respiratory infection. Now used to prevent
and cure the common cold. Active ingredients unknown. Can cause minor digestive
problems and rashes. Some harmful drug interactions.
Good-quality research is sparse. A recent analysis of 17 trials proved
inconclusive due to widespread methodology problems (Pharmacotherapy,
vol 20, p 690). Another review looked at 16 trials (鈥淓chinacea for preventing
and treating the common cold鈥�, Cochrane Database of Systematic Reviews)
and reported that some preparations may be more effective than placebo.
Ginkgo
Extract of the leaves of the Ginkgo tree (Ginkgo biloba). Ayurvedic
healers add it to longevity elixirs. It鈥檚 now used for a range of cognitive
problems including amnesia, loss of concentration, mild dementia, tinnitus and
vertigo. Also used against macular degeneration and arterial disease. Contains
two groups of chemicals with different effects: flavonoids, which act as
antioxidants; and ginkgolides, which inhibit blood clotting. Occasionally causes
bleeding, nausea and headaches. Some harmful drug interactions.
Research paints something of a confused picture thanks to the mass of
purported health effects. One recent review concluded there is good evidence it
helps with memory loss, dementia and hardening of the arteries (Antioxidants
& Redox Signalling, vol 1, p 469). A second reported that it improves
memory, concentration and alertness, and reduces tinnitus (Public Health
Nutrition, vol 3, p 495). An analysis of 8 trials found it superior to
placebo in treating aterial disease of the legs, though the effects were modest
(The American Journal of Medicine, vol 108, p 276). Another study
examined macular degeneration and found no evidence in its favour (鈥淕inkgo
biloba extract for age-related macular degeneration鈥�, Cochrane Database
of Systematic Reviews).
St John鈥檚 Wort
An extract of the herb Hypericum performatum. Described by
Hippocrates as a cure for demonic possession. Used to treat mild to moderate
depression. Contains more than two dozen potentially active ingredients, most of
which haven鈥檛 been properly studied. In common with other antidepressants, it
has numerous side effects including dry mouth, headaches, constipation,
palpitations, sweating and nausea. Users who expose themselves to bright light
can develop cataracts. Some harmful drug interactions.
St John鈥檚 Wort is well researched. Two recent studies conclude that it is
better than placebo and at least as good as tricyclic antidepressants (
British Medical Journal, vol 319, p 1534 and vol 321, p 536). Questions
remain about its long-term effects and how it compares with modern drugs. A
review of 27 trials found it significantly better than placebo but called for
further studies (鈥淪t John鈥檚 Wort for depression鈥�, Cochrane Database of
Systematic Reviews). However, it is ineffective against severe depression
(The Journal of the American Medical Association, vol 285, p 1978).
Saw Palmetto
An extract of the berries of the North American palm Serenoa repens.
Used to treat benign enlargement of the prostate gland. Studies show that it
inhibits the conversion of testosterone to dihydro-testosterone, the hormone
thought to cause prostate enlargement. No side effects or serious drug
interactions.
It appears to work. A review of 18 trials concludes that its effect is
comparable to the synthetic drug Proscar (The Journal of Urology, vol
163, p 1451). However, its long-term effectiveness and safety are unknown.