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He stresses that drinking coke doesn't replace his amitriptyline tablets - the daily pain medication he takes to try to prevent migraines - but it does sometimes help him "last until the end of the day".

The results, published today in The Lancet, showed that patients taking amitriptyline were almost twice as likely to report an overall improvement in symptoms as those taking a placebo.

Among the drugs studied - which included Prozac and a cheap antidepressant called amitriptyline - only one, called duloxetine, showed any evidence for pain relief.

The researchers randomized the children into three groups that received a placebo, the antidepressant amitriptyline or the antiepileptic medication topiramate.

The 500 test patients will be given either amitriptyline or a placebo tablet for six months and their symptoms and mood checked regularly.