"We would never encourage irresponsible marketing of St John's Wort, " he told the BBC.
John's Wort grows wild in parts of Europe, where scientists have been studying it for decades.
John's Wort is just as helpful as drugs, with none of the side effects, such as headaches or vomiting.
The flax-leaved St John's Wort is now spreading at Craig y Dre in Tremadog, according to Natural Resources Wales (NRW).
BBC: St John's Wort boosted by Gwynedd cliff scrub clearance
So to discover that a plant like St John's Wort has pharmaceutical properties does not rock me back on my heels.
The recent clinical trial the doses of the St John's Wort extract were similar in size to pharmaceutical doses of antidepressant.
St John's Wort has been used for many years in folk medicine to treat disorders such as burns, wounds and depression.
John's wort, a popular herbal remedy used primarily to treat mild depression.
John's Wort may not be well known in the United States, doctors in Germany prescribe for depression, and insurance pays for it.
John's Wort might be just as effective, and with fewer side effects.
John's wort are safe, but this study demonstrates that there can be dangerous interactions when taken with other drugs prescribed to treat medical conditions.
And since no patent can be issued on Ginko Biloba or St John's Wort, there is no advantage to any company which pays to test natural drugs.
John's wort, the authors of the review found "good but limited" evidence for the anxiety-reducing effects of supplements containing L-lysine and L-arginine, two amino acids produced naturally by the body.
But Dr Ann Walker, senior lecturer in human nutrition at the University of Reading and a qualified medical herbalist, said the findings would make little difference to the average St John's wort user.
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