WASHINGTON (AP) — The Veterans Affairs Department is sending letters to about 33,000 veterans who are taking the anti-smoking drug Chantix, warning them about possible side effects, including thoughts of suicide.

VA Secretary James Peake told reporters in a conference call Thursday that agency doctors will continue to prescribe the drug because they are seeing no serious problems or trends with its use.

He defended the VA's use of the drug to treat some of the veterans with stress disorders who were participating in a study to stop smoking. Of the 143 veterans with post-traumatic stress disorder who took Chantix in the study, he said that three — or 2 percent — experienced thoughts of suicide. Of the roughly 800 veterans in the study who did not take Chantix, 35 had suicidal thoughts — or about 4.4 percent, he said.

The letter going out to the veterans Thursday urges anyone who is experiencing side effects or is worried about continuing to use the drug, to consult with their doctor.