SYDNEY, May 8  - Prescription rates for ADHD vary widely both within and across states, with the highest rate of prescriptions 75 times more than the lowest rate, according to data presented at the Royal Australasian College of Physicians (RACP) annual Congress in Melbourne on Monday.

The first Australian Variation in Healthcare Atlas shows NSW had the highest rate of prescription at 13,588 per 100,000 children aged 17 or under.

South Australia had the lowest usage with 5,541 per 100,000 children. 

Professor Harriet Hiscock from the Royal Children's Hospital Melbourne says the prescription of ADHD medication is a complex issue and doctors aren't just to blame for the variations. 

"Often prescribing doctors - in this case paediatricians and child and adolescent psychiatrists - are called out as the key factor as to why variations exist. My research suggests that there are multiple reasons as to why this is happening."

One of those factors is inequitable access to psychologists, Prof Hiscock suggests.

"If we just look within Victoria, for example, we know that children in low socio-economic areas are more likely to meet criteria for ADHD but we are not necessarily seeing more prescribing in those areas, so there is a mismatch between prescribing and where we think kids with ADHD live," she said.

While Medicare does partly reimburse families for up to 10 visits to a psychologist every year, it doesn't always cover the costs.

"Anecdotally we are hearing that those families will therefore space out those appointments with a psychologist to be able to afford to see them and we know for some kids they're not getting enough therapy and time, it becomes too diluted," she said. 

ADHD is estimated to affect seven per cent of all Australian school children and the decision to medicate a child has attracted much debate.

At this stage, it's too early to say if the variation in medication use is a good or bad thing, says Prof Hiscock.

"That's a big elephant in the room," she acknowledged.

"What we lack in Australia is good outcome data for these kids, so we can't actually say at the moment if some kids are being under-treated or over-treated," Prof Hiscock said.

However there is some evidence, she says, that shows medication can be beneficial.

"The international data would suggest that certainly for kids with moderate to severe ADHD if you don't treat them then they are more likely to drop out of school and end up in drug and crime related activity. They are also more likely to end up in emergency departments with injuries and accidents if they are not on medication," said Prof Hiscock.

The Royal Australian and New Zealand College of Psychiatrists says deciding to prescribe kids with antipsychotic drugs is always taken with great care and after thorough discussions with parents.