A doctor warned musician Carter Albrecht he might lose his soulful sound if he didn't ditch cigarettes. He asked his girlfriend about the stop-smoking drug Chantix.

"And then we decided that we would do it together because we decided that we wanted to quit," said Ryann Rathbone.

Rathbone says almost immediately, they both started having vivid, often frightening dreams, a known side effect.

"Nightmare kind of… hallucination kind of dreams where you don't know if it's real or not," she said.

A week later, after an evening of cocktails, Albrecht started hallucinating for real.

"And the things that he was saying did not make any sense. It was like he was in a nightmare," said Rathbone.

The nightmare ended with a terrified 911 call after a neighbor shot Albrecht dead.

"I was thinking there's no way. There's no way. There's no way. It doesn't make any sense. None of it does," said Rathbone.

Months before Carter Albrecht's bizarre death, bloggers had started posting concerns about Chantix.

"I thought I was losing my mind" wrote one. Another told of a "super depressed meltdown."

One man said the dark feelings came out of the blue for him too, after having a few drinks with his wife.

"So you mix a drug that affects the central nervous system, like Chantix, and you mix a drug like alcohol that affects the central nervous system. It's possible to have some unusual kind of responses," said Dr. Bryon Adinoff, and addiction psychiatrist.

But Dr. Richard Honaker says he's urging caution with Chantix, but believes the risk may still be worth the benefit.

"More patients by far are able to quit smoking with this drug than anything else we have," he said.

Ryann Rathbone has gone public with her grief.

"I definitely want people to learn from his death," she said.

The Chantix label does contain a warning not to mix it with alcohol.

Pzifer, the maker of Chantix, has said clinical studies don't suggest that Chantix use leads to rage.

Statement from Pfizer regarding its stop-smoking medication, Chantix

Pfizer is committed to ensuring patient safety and regularly monitors and evaluates any adverse events reported to Pfizer either directly or indirectly through secondary sources. We routinely conduct reviews of post-marketing safety surveillance data, and that data to date do not suggest a causal relationship between the use of Chantix (varenicline) and violent behavior. Pfizer's prescribing information for Chantix notes that in clinical trials, the following adverse events were among those reported in Chantix patients on an "infrequent" basis (which is defined as occurring in between 1 in 100 and 1 in 1,000 patients): aggression, agitation, mood swings and abnormal thinking. The rate of occurrence of these adverse events in the clinical trials among patients treated with Chantix was comparable to those taking placebo. It is important to note that a vast body of medical literature has shown that smoking cessation, with or without treatment, is associated with nicotine withdrawal symptoms and has also been associated with the exacerbation of underlying psychiatric illnesses. In May 2007, Pfizer updated the Chantix U.S. prescribing information to reflect this information.