A study linking medical marijuana to an increase in recreational use has been criticised for failing to take into account the additional benefits of medical marijuana laws, such as a reduction in the use of opioids.

The research published in JAMA psychiatry found cannabis use and abuse or dependence in adults increased between 1991-92 and 2012-13 to a significantly greater extent in US states with medical marijuana laws compared to those states without.

The increased use may reflect factors such as easier access, increased potency, perceived safety or acceptability and generally more permissive attitudes, the researchers said.

 They concluded that while medical marijuana laws may benefit some patients, its availability might also have adverse public health consequences.

“A prudent interpretation of our results is that professionals and the public should be educated on risks of cannabis use and benefits of treatment, and prevention/ intervention services for cannabis disorders should be provided,” they wrote.

However alcohol and drug expert Dr Alex Wodak told the limbic the differences between the states in terms of cannabis use or disorders – of the order of 1% – were very small.

He said the findings were unlikely to have implications for Victoria – the first Australian state to legalise cannabis for medicinal use in patients such as children with severe, intractable epilepsy.

Dr Wodak, president of the Australian Drug Law Reform Foundation, said the US study failed to mention evidence of additional benefits from medical marijuana.

He said a 2014 study had shown death rates from overdoses associated with analgesic opioids were 25% lower in states with lawful medicinal cannabis than in other states.

“Two or three studies have since found where medicinal cannabis is lawful, people use lower doses of opioids for severe, chronic pain and are topping up with medicinal cannabis.”

Dr Wodak said many doctors and medical associations in Australia were at best ambivalent about medicinal cannabis but should be more open-minded.

“Medicinal cannabis is not a panacea and not curative but it is a useful palliative drug, as a second line medication, especially in patients with a short life expectancy.”

He said where evidence of benefit was lacking it was because decades of regulatory obstacles had blocked access to research funding, ethics approval and cannabis samples to test.

Cannabis should be regulated and readily available to people with ‘a strong compassionate case’, he said.

“Most people obtain medicinal cannabis from the black market with associated legal risks, sky high prices, a total absence of quality control, the possibility of contamination with pesticides and heavy metals, and variability between batches.”