A large-scale survey in pro-cannabis US states has found no significant increase in problems from medicinal use.

According to the report on over 500,000 US adults between 2002 and 2014, there was no increase in the overall prevalence of marijuana use disorders (marijuana abuse or dependence), despite usage increasing overall.

But the researchers say that as an increasing number of US adults use marijuana, fewer people perceive the drug as harmful, so there could be a need for improved education and prevention messages regarding the risks of marijuana.

The authors also noted that the study did not look at use among children or teenagers, or the link between marijuana use and other more severe psychiatric disorders.

Even so, from the data on 596,500 adults aged 18 or older who took part in the annual US National Survey on Drug Use and Health (NSDUH) from 2002 to 2014, marijuana use (at least once in the previous year) increased from 10.4 per cent in 2002 to 13.3 per cent in 2014.

The proportion of adults who first started using marijuana in the previous year increased from 0.7 per cent in 2002 to 1.1 per cent in 2014.

The prevalence of daily or near daily use (defined as people who reported using marijuana on average 5 days or more per week) increased from 1.9 per cent to 3.5 per cent over the same period.

But at the same time, the prevalence of marijuana use disorders (abuse or dependence) among adults in the general population remained stable at about 1.5 per cent between 2002 and 2014, and the prevalence of marijuana use disorders among users declined (14.8 per cent to 11 per cent).

People who used marijuana were more likely to develop dependence if they were male, younger, had low education, were not in full time employment, had depression and used tobacco or other substances.

The full report has been published in The Lancet Psychiatry.