That was the sad situation for a 23-year-old Corrimal man, whose doctor told him he had to choose between losing the weight or his sanity.

Ryan* was just a teenager when diagnosed with schizophrenia and placed on Olanzapine, an anti-psychotic medication.

It was the only treatment that enabled him to overcome the symptoms of schizophrenia, including hallucinations and the inability to comprehend the world around him. But it caused debilitating physical side effects.

University of Wollongong (UOW) scientists could be the first in the world to break down the drug, eliminating the horrific side effects while maintaining the compounds that help thousands of mental health patients worldwide.

The breakthrough could also reduce the rate of type 2 diabetes among schizophrenia sufferers, who have the highest rate compared to any other group - 25 per cent.

Those on anti-psychotic medication such as Olanzapine had rates as high as 34 per cent, according to Schizophrenia Fellowship NSW chief executive officer Rob Ramjan.

"If you could find a way to keep the weight gain under control, we'd not just be giving people a better quality of life, you're also going to be reducing the risk of type 2 diabetes. So this is really, really important," he said.

Olanzapine is among the most effective mental health drugs available, but most of its users gain substantial weight.

UOW Medical Research Institute director Professor Don Iverson said the drug probably altered the patient's metabolism.

The university's Prof Xu-Feng Huang has modified the drug and Dr Elisabeth Frank is now leading laboratory tests.

Ryan weighed a healthy 82kg when diagnosed with schizophrenia at 16 but nearly doubled his weight within eight months of taking Olanzapine.

He saw a trainer three times a week but couldn't lose the kilos. "It demotivated me, it made me crave lots of food, it slowed my metabolism," he said.

As his frame grew, his self-esteem and confidence shrank. But without the medication, Ryan said he would have been unable to communicate socially or improve his schizophrenia. *Not his real name.