Oxytocin - the so-called ''love hormone'' - may not improve the symptoms of children with autism, a new study has found.
Previous findings have shown that the brain chemical, known to encourage trust and social bonding, could have benefits for children with the disorder, said research leader Professor Mark Dadds, a psychologist at the University of NSW.
In recent years, the use of ''oxytocin to treat autism symptoms has become a worldwide phenomenon'', Professor Dadds said.
Some parents, he said, are buying it ''semi-illegally'' over the internet in the hope it will help treat their children with the disorder.
But the latest study - the largest of its kind worldwide - has cast doubt over the use of nasal spray oxytocin as a possible treatment.
''Our study is the first one to show it had no effect,'' Professor Dadds said. ''It's a very important finding because there are at least 20 similar studies going on now.''
Professor Dadds conducted the clinical trial of 38 boys with autism, aged between seven and 16. Half were given a nasal spray of oxytocin on five consecutive days and half were given a placebo.
''We monitored the outcomes on social interaction, repetitive behaviour, their language and ability to read faces. It had no effect at all. We were so shocked we even took our oxytocin bottles to an independent lab to be tested. We thought something had gone wrong.''
He said the results may differ from previous studies because children with autism could have ''different genetic systems'' so the hormone becomes ineffective.
Oxytocin, released in brains of all mammals, is known for its use to induce labour and to regulate emotions.
''When you hug someone you get a burst of oxytocin,'' Professor Dadds said. ''It controls love, attachment and the ability to read what someone is thinking.''