Medicinal plants still comprise a nebulous cloud in biomedical science. We know they have been used since the dawn of man, but there are precious few good quality scientific studies that support their use. Unlike pharmaceutical drugs, plant medicines consist of many different molecules that interact together in the body to have a variety of, poorly understood, pharmacological effects. Despite variably successful attempts to identify single molecules in plants for drug development, we should acknowledge that the whole is greater than a single part. There is an increasing number of clinical studies which strongly imply that root, leaf, and flower extracts of medicinal plants can influence the brain and are effective at treating cognitive disorders. This article series will examine plants where we have double-blind, placebo-controlled studies to support their medicinal influence on the human brain.
St. John’s wort is a commonly known plant that is native to Europe and yields bright yellow flowers. Its name comes from flowering around St. John’s day on the 24th June. St. John’s wort has been used as long ago as the ancient Greeks, and the physician Dioscorides (40–90AD) used it in the treatment of sciatica. However, St. John’s wort has become known as less of a treatment for nerve pain and more so for depression, with multiple double-blind, placebo-controlled trials confirming its antidepressant properties. Authors typically compare St. John’s wort with mainstream anti-depressant drugs and find it has a preferable side effects profile. It is not without its downsides however, as excessive use has been linked to serotonin syndrome, sun sensitivity, and easy skin burning, and more generally with increased pharmaceutical drug metabolism by the liver. This means St. John’s wort may not be suitable for applications alongside other pharmaceutical drugs, and it is contraindicated with serotonin reuptake inhibitors.
American skullcap is a member of the mint family that is native to North America and grows wild in meadows and swamps. It was used by the Native Americans as a sedative and America’s 19th century physicians, the Eclectics, widely used the herb for complaints involving an overactive nervous system such as insomnia, anxiety, and epilepsy. A human double-blind, placebo-controlled study supports skullcap’s application against anxiety, and a mood elevating effect has also been noted. Herbalist’s view both St. John’s wort and American skullcap as ‘nervine tonics’, meaning that they act upon the nervous system medicinally and are also considered to have a long-term renewing effect. While, this claim is yet to be verified by scientific studies, it certainly warrants further investigation.
Ashwagandha, the root of which is a popular home remedy in India, is a plant native to India that is mentioned in the traditional Ayurvedic medical text, the Charaka Samhita, approximately 2000 years ago. Here it is recommended as a tonic for emancipation, reproductive ability, and longevity. In Ayurveda, it is classified as a ‘rasayana herb’, a class of plant that are considered to restore and support long-term health and that overlaps to some degree with the Western definition of a ‘tonic herb’. Two double-blind, placebo-controlled human studies support ashwagandha’s role in the reduction of anxiety. It’s wide-ranging medicinal properties are supported by two additional well-controlled, human clinical studies on osteoarthritis and subclinical hypothyroidism. The emerging picture is that ashwagandha possesses a wide range of medicinal properties that will likely be better understood in the future. Ashwagandha has been well-tolerated across clinical trials, with a side effect profile similar to placebo.
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