Is Stop-Smoking Drug A Suicide Risk?

Thirty-three year old Amy Garza has smoked since she was 16, trying time and time again to quit.

"I've tried just about anything and everything you can think of," she said.

She thought she had found a wonder drug this fall: Chantix, the new anti-smoking pill prescribed by her doctor.

Then, "it was like a psychotic breakdown that came out of nowhere," Garza said.

She told CBS News correspondent Thalia Assuras that she tried to kill herself. She has a large scar on one wrist to prove it.

Garza, who says she's never been under psychiatric care, blames Chantix, made by Pfizer.

"You really think it was because of this drug?" Assuras asked.

"I do," Garza said.

Garza isn't the only one. The FDA is investigating about 100 cases of smokers who had suicidal thoughts after taking Chantix.

It went on the market in 2006 using a new approach to kick the habit.

Chantix is the only stop-smoking product that blocks the nicotine receptors in the brain, eliminating the urge to light up. However, nicotine withdrawal itself can change behavior. So is Chantix to blame for thoughts of suicide?

"There's no scientific evidence establishing a causal relationship between Chantix and these reported events," said Dr. Ponni Subbiah, vice president of Pfizer's medical affairs.

Among the four million Americans prescribed the drug, there are big fans. Take David Bowers, a 30-year-old smoker who went on Chantix after developing Coronary Artery Disease.

"I thought it was a miracle drug," he said.

Clinical studies show that a year after taking the drug, 23 percent were not smoking. On Zyban, the only other prescription pill available, only 15 percent succeeded.

For now the FDA says the benefits of quitting cigarettes far outweigh the possible risks of taking Chantix. But the agency is still warning that anyone who uses Chantix should be closely monitored.