St John's Wort, the herb widely used to treat depression, may help patients with Raynaud's syndrome, a condition that makes sufferers' fingers and toes go white and numb.
In a new Canadian trial, patients will take three 300mg tablets, three times a day for six weeks. It is hoped the herb will not only decrease the frequency of attacks, but also the duration and severity.
Raynaud's is thought to affect around 10 million Britons. It occurs when the blood vessels that supply blood to the skin temporarily narrow. In some cases it may be linked to medication such as beta-blockers, but mostly there is no apparent cause.
Treatments often include antidepressants. These act on the brain chemical serotonin, which is known to narrow blood vessels.
St John's Wort also acts on serotonin.