A small yet world-first clinical trial at Deakin University has found an antibiotic used mostly to treat acne can help people with major depression.

An antibiotic used mostly to treat acne has been found to improve the quality of life for people with depression.

Researchers at Deakin University took a biological approach to treating major depression by adding a daily dose of minocycline - a broad-spectrum antibiotic that has been prescribed since 1971 - to the usual treatment of 71 people with the illness.

According to the results published in the Australian & New Zealand Journal of Psychiatry, patients taking minocycline reported improved functioning and quality of life.

There was also a trend towards a reduction in anxiety symptoms.

The trial support evidence that people with major depressive disorder have levels of inflammation in their body, says lead researcher Dr Olivia Dean.

"Minocycline reduces brain inflammation in cell models, and thus we wanted to see if it was useful for people," said Dr Dean, from Deakin's Centre for Innovation in Mental and Physical Health and Clinical Treatment.

Further trials are needed, but Dr Dean hopes the results of their small study will improve and add to current treatment options.

In Australia, up to one in four people will experience depression over their lifetime.

"Current antidepressants are useful, but many people find a gap between their experience before becoming unwell and their recovery following treatment," Dr Dean said.

"We aim to fill this gap by providing new, biologically-based, treatments for depression," Dr Dean said.

The researchers are now in the process of applying for funding to expand the trial to a larger group.