DENVER — Five months after Colorado became the first state to allow recreational marijuana sales, the battle over legalization is still raging.

Law enforcement officers in Colorado and neighboring states, emergency room doctors and legalization opponents increasingly are highlighting a series of recent problems as cautionary lessons for other states flirting with loosening marijuana laws.

There is the Denver man who, hours after buying a package of marijuana-infused Karma Kandy from one of Colorado’s new recreational marijuana shops, began raving about the end of the world and then pulled a handgun from the family safe and killed his wife, the authorities say. Some hospital officials say they are treating growing numbers of children and adults sickened by potent doses of edible marijuana. Sheriffs in neighboring states complain about stoned drivers streaming out of Colorado and through their towns.

“I think, by any measure, the experience of Colorado has not been a good one unless you’re in the marijuana business,” said Kevin A. Sabet, executive director of Smart Approaches to Marijuana, which opposes legalization. “We’ve seen lives damaged. We’ve seen deaths directly attributed to marijuana legalization. We’ve seen marijuana slipping through Colorado’s borders. We’ve seen marijuana getting into the hands of kids.”