With more and more states across the US legalising marijuana, a lot of people are worried about the effect it might have on teenagers (won't somebody think of the children?!).

But a new survey of more than 216,000 adolescents across the country might help put some of those concerns to rest. The results have shown that, since marijuana has become widely legalised, the number of teenagers smoking weed is on the decline, and so are their pot-related problems.

At the same time, more adults are using the drug. Which kind of reminds us all that nothing's cool anymore once your parents are doing it

That said, the researchers think the issue is a lot more complex than that - as are most things in life. Just because the two are linked, it doesn't necessarily mean that marijuana legalisation has driven down weed use in teens - after all, correlation doesn't equal causation.

More likely, there's something else going on to help kids get support when they need it. "We were surprised to see substantial declines in marijuana use and abuse," said lead researcher Richard A. Grucza from Washington University in St. Louis.

"We don't know how legalisation is affecting young marijuana users, but it could be that many kids with behavioural problems are more likely to get treatment earlier in childhood, making them less likely to turn to pot during adolescence," he added. "Whatever is happening with these behavioural issues, it seems to be outweighing any effects of marijuana decriminalisation."

The research looked at data on drug use in people aged between 12 and 17 over a 12-year period.

It also investigated weed-related problems in teenagers - so, how many of them were becoming dependent on the drug, or were having relationship or school problems as a result of their drug use. 

In good news, they found that teenagers struggling with those issues had declined by 24 percent from 2002 to 2013. Medical cannabis was first legalised in 1996.

They also asked kids whether they'd used pot for the first time in the previous 12 months, and found that the rate fell by 10 percent between 2002 and 2013.

As we said before, it's very unlikely that this is all because marijuana has been legalised.

Over the same period, the researchers also noticed a reduction in behavioural problems, like petty crime, getting in fights, and selling drugs. And those two were connected - as kids became less likely to engage in problem behaviour, they were also less likely to have issues with weed later on.

That's good news, because it means that managing behaviour like that as early as possible could help parents and researchers prevent kids from getting into trouble with marijuana.

"It's likely that if these disruptive behaviours are recognised earlier in life, we may be able to deliver therapies that will help prevent marijuana problems - and possibly problems with alcohol and other drugs, too," said Grucza.

The best part about all of this? With marijuana rapidly becoming decriminalised around the country, we can finally talk about all of this more openly.

The research has been published in the Journal of the American Academy of Child & Adolescent Psychiatry.