President Barack Obama has said he does not think marijuana is more dangerous than alcohol "in terms of its impact on the individual consumer".
"As has been well documented, I smoked pot as a kid and I view it as a bad habit and a vice," he said in an interview with the The New Yorker Magazine.
"(It's) not very different from the cigarettes I smoked as a young person up through a chunk of my adult life. I don't think it's more dangerous than alcohol."
He added that smoking marijuana was "not something I encourage, and I've told my daughters I think it's a bad idea, a waste of time, not very healthy".
Mr Obama's government has given states permission to experiment with marijuana regulation, and laws recently passed in Colorado and Washington state legalising the drug ave gone into effect.
The US president said it was important for the legalisation of marijuana to go forward in those states to avoid a situation in which some people were punished and others were not.
He added that he was troubled at the disproportionate number of arrests and imprisonments of minority groups caught smoking marijuana.
"Middle-class kids don't get locked up for smoking pot and poor kids do," he said.
"And African-American kids and Latino kids are more likely to be poor and less likely to have the resources and the support to avoid unduly harsh penalties."
Mr Obama also stated that users should not be locked up for long stretches of time when people writing drug laws "have probably done the same thing. But he urged a cautious approach to changing drug laws, saying that people who thought legalising pot would solve social problems were "probably overstating the case".
"The experiment that's going to be taking place in Colorado and Washington is going to be, I think, a challenge," he said.
Ethan Nadelmann, executive director of the Drug Policy Alliance, praised Mr Obama's words, saying his use of the word "important" about the new Colorado and Washington laws "really puts the wind in the sails" of the movement to end marijuana prohibition.