A genetic test may help to monitor dose of psycho-stimulant drugs like Ritalin to ADHD children, revealed by Australian health expert.

Stimulant medications for ADHD - methylphenidate, known as Ritalin, and dexamphetamine - work by stimulating dopamine, a chemical which controls several brain functions and relays messages. International researchers have discovered a gene, called COMT, which controls how much dopamine each person produces.

About 50,000 Australian children are prescribed stimulants to treat attention deficit hyperactivity disorder (ADHD), but problems getting the dose right mean many are initially over-drugged. ADHD expert Professor Florence Levy, of The University of New South Wales's school of psychiatry, said "It has been very hard to predict how kids will respond to treatment".

Professor Levy has published a review of testing gene in children in the latest edition of the Australian and New Zealand Journal of Psychiatry.

Adults with one version of the gene produced lower dopamine levels and therefore needed higher doses of the stimulants for the drug to work. But those with the other version already had high levels and required only very small doses of medication.

"It might just be that we're able to predict how kids will react to the drug in advance, and save them from these fluctuations and overdosing of psycho-stimulant drugs like Ritalin to ADHD children during their ADHD therapy period.