Cannabis brings little benefits to those who suffer from PTSD. iStock

There is not enough evidence that using plant-based cannabis can help people who are suffering from post-traumatic stress disorder (PTSD). However, the legalisation of medical marijuana in many US states means that many patients will turn to it in the future – so more research is needed to assess the long-term health risks.

In recent years, there has been an ongoing debate about whether cannabis could help treat PTSD. Some studies have pointed out the prevalence of marijuana abuse among PTSD sufferers.

However, a small number of research papers have shown that cannabis could have therapeutic virtues for those patients affected by a range of debilitating symptoms, from emotional numbness and re-experiencing their trauma through nightmares, to irritation, anger and insomnia.

As a result, more than a third of patients who seek cannabis for medical reasons in the US states where it is legal now report that they are doing so to combat PTSD symptoms.

To settle the question about whether the plant can really help them, researchers have analysed the results of previous studies on the subject.

In a study now published in the Annals of Internal Medicine, the team reviewed data from two systematic reviews and three primary studies which had looked at the effects of plant-based cannabis preparation – but not synthetic cannabinoids – for treating PTSD.

They found that there was insufficient evidence to date to draw firm conclusions about the efficacy of cannabis in PTSD sufferers. It even appears that cannabis can in some cases lead to a degradation of patients' health.

Indeed, one of the largest observational studies of veterans with PTSD found a small but significant worsening of symptoms in patients who continued or started cannabis use, compared with patients who had never used it or stopped using cannabis during the study.

That being said, the scientists recognise that US states are unlikely to overturn medical indications from legislation of cannabis, so the priority is now to learn about the effects of cannabis on patients' symptoms, and to look in greater details as to whether there are long-term health risks.

"Even if future studies reveal a clear lack of substantial benefit of cannabis for pain or PTSD, legislation is unlikely to remove these conditions from the lists of indications for medical cannabis. It will be up to front-line practising physicians to learn about the harms and benefits of cannabis, educate their patients on these topics, and make evidence-based recommendations about using cannabis and related products for various health conditions. In parallel, the research community must pursue high-quality studies and disseminate the results to clinicians and the public," the scientists write in an editorial published in the same issue of the journal.