More adults are using cannabis since laws were introduced to legalize the drug, experts have revealed.

Meanwhile fewer teenagers are turning to the drug, there has been a decrease in marijuana-related arrests, but an increase in admissions for addiction treatment.

A team of scientists led by Dr Jane Maxwell from the University of Texas at Austin and Bruce Mendelson, of the Denver Office of Drug Strategy, reviewed data looking at how marijuana laws have affected rate of use of the drug.

In recent years a number of states have legalized possession and use of small amounts of cannabis, while several others have 'decriminalized' the drug.

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There has been a rise in adults using cannabis in the last 10 years, experts said. They attributed the rise to the fact 23 US states now have laws legalizing the drug in some form

As of June last year 23 states and the District of Columbia currently have laws legalizing marijuana in some form.

Cannabis is legal of recreational use in Washington state, Oregon, Alaska and Colorado as well as the District of Columbia.

The drug is legalized for medical use in California, Nevada, Arizona, New Mexico, Montana, Minnesota, Illinois, Michigan, New York, New Jersey, Delaware, Maryland, Connecticut, Rhode Island, Massachusetts, Vermont, New Hampshire and Maine.

Data from the National Survey on Drug Use and Health reveal that, over the past decade, marijuana use has increased significantly among adults aged 18 to 25, and those aged 26 and older.

Dr Maxwell and Mr Mendelson note these trends could have begun before 2012, when Colorado and Washington became the first states to legalize the drug.

Meanwhile, cannabis use by young people aged 12 to 17 has not seen the same increase.

However, young people's perceptions of the risks of using marijuana have decreased, suggesting they may be more likely to using the drug in the future.

Studies have consistently shown the potency of cannabis is increasing.

Data from California suggests that marijuana is more widely available, and that more drivers are testing positive for it, the authors said.

Initial reports from Colorado and Washington state also provide evidence on the impact of legalizing the drug.

In Denver, marijuana-related hospital admissions, emergency department visits, and calls to poison control centers have all increased.

Cannabis is more widely available in California, where it is legalized for medical use, and more drivers are testing positive for the drug. Marijuana-related hospital admissions and ER visits have all increased in Denver, Colorado, where the drug is legal for recreational use

At the same time, arrests for marijuana use and, or possession and admissions to substance use disorder treatment programs have decreased.

Furthermore in Seattle, data reveals reduced rates of treatment admissions and police involvement, along with an increased prevalence of frequent cannabis use.

The authors said: 'As more states enact laws allowing the medicinal use of marijuana and relax penalities for the personal use of marijuana, attention should be paid to the experiences of the states to date, and changes in their laws to handle unanticipated problems.'

They added: 'Data is needed to understand the relationship between the patterns and amounts of use in terms of consequences as well as data on the health conditions of those receiving medical marijuana and the impact of higher potency.'

The authors note there is a lack of data on the characteristics of users of medical cannabis, their medical conditions and use patterns.

There is also a knowledge gap regarding adverse effects of medicinal marijuana, and the adverse events users may suffer by using different variations of the drug.

They said more studies are needed to understand the relationship between the patterns and amounts of use in terms of consequences, as well as on the health conditions of those receiving medical marijuana and the impact of higher potency.