The US government has offered guidance to banks that want to accept deposits from marijuana sellers, lowering their risk of prosecution.
Under the policies, cannabis sellers in states with medical or legal marijuana will have access to banking services.
Currently, sellers deal almost entirely in cash, increasing the risk of robbery and the ease of money laundering.
Colorado and Washington State voted in 2012 to legalise cannabis. Other states are expected soon to follow.
"We hope today's guidance will give banks the comfort they need to begin doing business with the legal marijuana industry in Colorado," Michael Elliott, executive director of the Marijuana Industry Group, a trade organisation, said in a statement.
The changes out of Washington DC reflect the shift in political attitudes toward the drug, says the BBC's Rajini Vaidyanathan in Washington.
At present, federally insured banks which take deposits from the proceeds of marijuana sales risk drug racketeering charges.
Green cash crop
Green cash crop
“If you trust in yourself, and believe in your dreams, and follow your star. . . you'll still get beaten by people who spent their time working hard and learning things and weren't so lazy.”
Re: Green cash crop
Making it easier for the tax man to cometh might be part of the motivation of the new policies as well.