Using sophisticated brain imaging techniques, US researchers have concluded that Ritalin (methylphenidate), taken by millions of children worldwide, exerts the same effect on the brain as cocaine.

Brain scans of 11 healthy men who took various oral doses of Ritalin showed that the dosage typically given to children - 0.5 mg - blocked 70 per cent of the dopamine transporters that remove excess dopamine from the system (cocaine typically blocks 50 per cent).

Dopamine is a chemical messenger that sends a message to the brain that a particular experience is pleasurable and worth repeating. An oversupply of dopamine can lead to overstimulation and even addiction.

Struggling to understand why Ritalin doesn’t appear to produce either addiction or a ‘high’ in those with attention deficit/hyperactivity disorder (ADHD), researchers theorise that such users may have more dopamine tranporters preventing excess dopamine from stimulating the pleasure circuits of the brain.

This, they say, may explain why usually interesting activities provide little pleasure or rewards for children with ADHD, causing them to be easily distracted.

Studies have shown that children with ADHD who took Ritalin may be more prone to drug addiction than those who didn’t take the drug. Ritalin may also alter the whole biodynamic profile of its users and cause the same devastating effects as long-term cocaine use (J Neurosci, 2001; 21: RC121).