It's hardly the most impressive claim made for valerian, but the plant seems to hold the world record for having the most names. Valeriana officianalis - a widespread perennial herb with white, pink or lavender flowers - is also known as all-heal, blessed herb, capon's tail, heliotrope, setwall, St George's herb, tagara, tobacco root and vandal root. Even its simple name, valerian, is variously prefixed Belgian, cat's, common, English, fragrant, garden, German, great wild, Indian, Mexican, Pacific, Vermont and wild. However, American valerian, or lady's slipper, is a totally different herb with no medicinal qualities.
The most appropriate name for the plant is phu (pronounced pooh). It is probably a coincidence, but the dried root of valerian - the part used in modern extracts - has an odour that some have compared to dirty socks. Cats become frisky after smelling it, and an oil prepared from valerian and aniseed is used by Gypsies to pacify dogs. Horses, too, are known to like its smell - as are rats and mice, hence its historical use as a bait in traps.
Its main application, however, has always been medicinal. Valerian was used in ancient ayurvedic medicine and by the Chinese. In his Complete Herbal, the 17th-century apothecary Nicholas Culpeper declared that "The root of valerian boiled with liquorice, raisins and aniseed is singularly good for those that are short-winded and for those that are troubled with the cough, and helps to open the passages and to expectorate phlegm easily." It is also useful for expelling "the wind in the belly".
Modern-day herbalists make similar claims - that valerian extract (whether in tea, tincture, capsule or tablet form) is suitable for the treatment of colds, fevers, shortness of breath and wheezing. However, the herb is most widely prescribed for insomnia. Once referred to as "the Valium of the 19th century", it was later used to treat shellshock victims in the first world war, and is now one of the most popular over-the-counter remedies in Europe. The key to its sedative qualities lies in a group of ingredients called valepotriates. One of these, valerianic acid, inhibits the breakdown of the brain chemical gamma-amino butyric acid - a natural tranquilliser. Valerian also contains essential oils that are believed to depress the central nervous system, plus alkaloids (chatrine and valerianine), glucosides, formic acid, acetic acid, starch, resin and various trace minerals.
In 1996, researchers at the Psychiatric University in Basel, Switzerland, found that valerian extract was as effective as benzodiazepines in treating insomnia, but had markedly fewer side effects. Half the benzodiazepine group complained of unpleasant symptoms, compared to just 10% of the valerian group. Various clinical studies have shown that a standardised extract of valerian - taken in doses of up to 900mg, one hour before bedtime - improves sleep quality without causing grogginess the morning after. Taken in smaller doses (400mg), it has been shown to relieve stress and anxiety.
But valerian is not without its drawbacks. First, it can take two or three weeks for the herb's sedative effects to be noticed, making it unsuitable for acute insomnia. Second, like synthetic tranquillisers, it should not be taken with alcohol, when pregnant or breastfeeding, or when driving or operating machinery. Third, large doses over long periods can cause headaches, giddiness, blurred vision, restlessness, nausea and symptoms of poisoning. As a guide, a nightly tea or infusion should be taken for no longer than three weeks at a time, and a nightly capsule or tablet for no longer than six months. No cases of drug interaction have been reported, but valerian lowers blood pressure and may exacerbate the effects of anaesthetics and medicines taken for high blood pressure. Animal studies suggest that valerian also increases the effects of benzodiazepine and phenobarbital tranquillisers. Anyone taking conventional drugs for hypertension, sleeping pills or sedatives should consult a GP before trying valerian extract.
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