PEOPLE using the herb St John鈥檚 wort as an antidepressant should take extra
care if they go out in the sunshine to cheer themselves up. A combination of the
popular herbal remedy and bright light can lead to cataracts, researchers told a
meeting in Washington DC last week.
Hypericin, the active ingredient in St John鈥檚 wort, reacts with visible and
ultraviolet light to produce free radicals. In laboratory experiments, Joan
Roberts of Fordham University in New York and her colleagues showed that this
reaction can damage proteins in the eye that give the lens its transparency. 鈥淚f
the proteins are damaged, they precipitate out of solution and make the lens
cloudy,鈥� says Roberts. 鈥淭hat鈥檚 what a cataract is.鈥�
However, hypericin did not cause any protein damage when kept in the dark,
the researchers reported at a meeting of the American Society for Photobiology.
Roberts recommends that those taking St John鈥檚 wort should wear hats and
wraparound sunglasses. 鈥淚f this product is consumed, one should avoid exposure
to bright light to prevent damage to the eye,鈥� she says.
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The side effect may be a particular problem for any sufferers of seasonal
affective disorder (SAD), who combine St John鈥檚 wort with light-box therapy.
鈥淐ertainly never take this drug and use light therapy,鈥� says Roberts. But she
cautions that all users should be warned of the risks, particularly if taking
the herbal treatment at the beach or while skiing.
Ivor Roots, a clinical pharmacologist at Humboldt University in Berlin,
agrees that people must exercise caution when using the herb. 鈥淥ne should not
assume that herbal drugs are not without potential side effects,鈥� he says. 鈥淚n
Germany, it is recommended to avoid tanning beds while taking St John鈥檚
飞辞谤迟.鈥�
Cows grazing on St John鈥檚 wort flowers are known to suffer from extreme
photosensitivity that can prove fatal, according to Roots. When exposed to
bright sunlight for long periods, the animals develop inflamed and swollen
tissues that make swallowing and breathing difficult.
David Wheatley, a psychiatrist at the Charter Chelsea Clinic in London, says
he has had no complaints from his patients about side effects while taking St
John鈥檚 wort. 鈥淚t works extremely well for people with mild to moderate
depression,鈥� he says.
But Geoffrey Bove, a neurophysiologist at Harvard Medical School, has treated
a patient who developed intense pain in areas exposed to the sun while taking St
John鈥檚 wort (The Lancet, vol 352, p 1121). Bove believes that free
radicals generated by hypericin resulted in the damage to the patient鈥檚 nerve
cells.
There may be a silver lining lurking in the herb鈥檚 side effect, however.
Hypericin鈥檚 strong reaction with light is currently being investigated as a
treatment for some skin cancers. 鈥淚ts side effect is being used as a potential
therapy for killing cancer cells,鈥� says Roberts.