Dr. McFall says the VA decided to continue the Chantix study because "it would be depriving our veterans of an effective method of treatment to help them stop smoking."
Caplan, one of the country's leading medical ethicists, said he was stunned by the VA's decision to continue the Chantix experiment.
"Why take the group most a risk and keep them going? That doesn't make any sense, once you know the risk is there," he said.
Chantix is one of the drugs being used in an estimated 25 clinical studies using veterans by the VA.
Pfizer maintains that "the benefits of Chantix outweigh the risks" and that it continues to do further studies on the drug.
The FAA has prohibited commercial airline pilots from using Chantix because of its possible side effects.