Hickenlooper was asked during a gubernatorial debate about other state governors who may be considering legalizing marijuana.
"I would view it as reckless before we see what the consequences are" in Colorado, Hickenlooper said, International Business Times reported. His Republican challenger, Bob Beauprez, agreed with the "reckless" characterization, according to Politico.
Hickenlooper later expanded on Colorado's legalization, saying: "I think for us to do that without having all the data, there is not enough data, and to a certain extent you could say it was reckless.
"I'm not saying it was reckless, because I'll get quoted everywhere," Hickenlooper added. "But if it was up to me, I wouldn't have done it, right. I opposed it from the very beginning. All right, what the hell -- I'll say it was reckless."
Kathy Green, interim spokeswoman for the governor, later explained: "In the face of inaction from the federal government, Colorado voters had no choice but to act on their own. While the governor believes it was reckless for Colorado to be the first state to violate federal drug laws, it is clear that Colorado voters saw no other choice -- and we are committed to carrying out their will, as democracy demands."
Hickenlooper has said in the past that he "hates" that Colorado is the "experiment" on marijuana legalization and has urged other governors to be cautious in considering reform laws. He also has said the drug war has been a "disaster" and he can see why so many people support reform.
Hickenlooper faces a tight race for re-election in November. It's not clear why he would bash a marijuana law approved by a strong majority of voters. The rollout of the law appears to be "succeeding" and most voters continue to support it, even though state regulation of marijuana sales isn't perfect.
"Politically, it’s a pretty reckless statement," Mason Tvert, a key backer of legalization, told The Huffington Post. "Gov. Hickenlooper was elected by 51 percent of the state’s voters, whereas 55 percent approved the marijuana initiative in 2012. Some of them might now be thinking they made a pretty reckless decision when they voted him into office."
Tvert added that he finds it odd that Hickenlooper, who was a beer brewer before becoming governor and made his fortune selling alcoholic beverages, would oppose legalization of a substance historically controlled by criminals and cartels.
Colorado and Washington are the only two states to have legalized recreational marijuana. Voters in Oregon, Alaska and Washington, D.C., will decide on legalization next month. Twenty-three states, including Colorado, have legalized marijuana for medical purposes.
This article has been updated to include the comment of the governor's spokeswoman.