A massive new study, examining the health records over almost 150,000 people, has found three commonly prescribed drugs, including statins used to lower cholesterol, can be associated with reduced rates of psychiatric events in those suffering from serious mental illness.

The study was conducted by an international team of researchers from University College London, Karolinska Institute Sweden, and the University of Hong Kong. Using Swedish medical records, 142,691 subjects were studied, all of whom had been previously diagnosed with either bipolar disorder, schizophrenia, or non-affective psychosis, and treated with psychiatric medication.

The researchers were looking to see if there was any correlation between episodes of self-harm or psychiatric hospitalization, and three common medications. The medications studied included statins for high cholesterol and heart disease, biguanides such as metformin for diabetes, and calcium antagonists used to treat high blood pressure.

The overall results were statistically significant with UCL researcher and lead author Joseph Hayes suggesting a between 10 and 20 percent reduction in psychiatric episodes for those subjects taking one of the three noted drugs, compared to those subjects not on any of the three medications.

"This study is the first to use large population data sets to compare patient's exposure to these commonly used drugs and the potential effects on people with serious mental illnesses," says Hayes. "Given these drugs are commonly used and well-known to doctors they should be further investigated as repurposed agents for psychiatric symptoms."

The usual causation versus correlation hazards of course apply when interpreting the results of a large epidemiological study such as this. Mental health experts are responding with cautious optimism, suggesting that while the study is relatively rigorous and well-designed, a more directed clinical trial will be vital before anyone could recommend these drugs be administered for mental health reasons.

"These remarkable results suggest that an entirely new class of medication – at least new in terms of mental health – may offer benefits," says Derek Tracey from the Royal College of Psychiatrists. "Given the burden of schizophrenia, these results pave the way for further testing of the impact of statins, ideally using a scientific randomized controlled test."

There are questions hovering over how each of these three drugs could be producing beneficial mental health effects. The authors of the new study hypothesize several potential mechanisms for psychiatric mechanisms, but at this point these prospective explanations are entirely up for debate. Naveed Sattar, from the University of Glasgow, is mildly skeptical the study can back up its conclusions with causal explanations.

"[The authors'] explanations for how these drugs may improve mental health are highly speculative," says Sattar. "So I would be strongly cautious with these findings and would only change my mind if effects are proven to be robust in a randomized trial setting."

The researchers behind the new study are in no doubt that further clinical study needs to be done to substantiate these observational conclusions. Nevertheless, these kinds of large longitudinal population studies can be incredibly valuable in uncovering associations that regular research could not reveal.

The new study was published in the journal JAMA Psychiatry.