Legalization activists in Colorado were frustrated after they tried and failed to get the president to take a stand on the state's marijuana measure during the presidential campaign in the battleground state.
"Here's the president, an admitted marijuana user in his youth, who's previously shown strong support for this, and then he didn't want to touch it because it was such a close race," said Joe Megyesy, a spokesman for a marijuana legalization group.
Megyesy said Obama's comments were "good news," but left unanswered many questions about how pot regulation will work.
Even if individual users aren't charged with crimes, pot producers and sellers could be subject to prosecution and civil forfeiture and other legal roadblocks, he said.
Marijuana is a crop that can't be insured, and federal drug law prevents banks from knowingly serving the industry, leaving it a cash-only business that's difficult to regulate, Megyesy said.
Colorado's Democratic governor, John Hickenlooper, said Obama's statements didn't settle questions about regulating pot.
"If the Justice Department and the president come together and together release a statement along those lines, it would certainly give us some clarity," he said.
Other states have been closely watching the developments in Colorado and Washington and how the federal government responds.
In Delaware, where a medical marijuana program has been put on hold amid concerns over fear of federal prosecutions of pot growers and distributors, Gov. Jack Markell's spokeswoman said his administration has the same concerns about legalization.
"If the federal government is saying it won't pursue persons with a medical need or recreational users, but it is prosecuting persons who provide that marijuana in a safe manner, then we are forcing people to obtain marijuana from the illegal market," Cathy Rossi said.
Wyatt reported from Denver. Associated Press writer Rachel La Corte in Olympia, Wash., and Randall Chase in Dover, Del., contributed to this report.