The guards at the Guantánamo Bay prison camp are the "overlooked victims" of America's controversial detention facility in Cuba, according to a psychiatrist who has treated some of them.

In some cases, a tour of duty at the camp has made guards suicidal and prompted a variety of psychiatric symptoms, from depression and insomnia to flashbacks. The guards' testimony also provides a harrowing insight into the treatment of prisoners.

Professor John Smith, a retired US Air Force captain, treated a patient who was a guard at the camp. "I think the guards of Guantánamo are an overlooked group of victims," Smith told the American Academy of Forensic Sciences annual meeting in Washington DC on Saturday. "They do not complain a lot. You do not hear about them."

The patient ('Mr H') is a national guardsman in his early 40s who was sent to Guantánamo in the first months of its operation, when prisoners captured in Afghanistan were beginning to flood into the camp. Mr H reported that he found conditions at the camp extremely disturbing. For example, in the first month two detainees and two prison guards committed suicide.

Painful positions

The taunts of prisoners and the things his superiors required him to do to them had a severe psychological impact on Mr H. "He was called upon to bring detainees, enemy combatants, to certain places and to see that they were handcuffed in particularly painful and difficult positions, usually naked, in anticipation of their interrogation," said Smith.

On occasion he was told to make prisoners kneel, naked and handcuffed, on sharp stones. To avoid interrogation the prisoners would often rub their wounds afterwards to make them worse so that they would be taken to hospital.

Some of the techniques used by interrogators resulted in detainees defecating, urinating, vomiting and screaming.

Mr H told Smith he felt profoundly guilty about his participation. "It was wrong what we did," he said.

The prisoners also threatened Mr H. "They would tell him they had networks of people throughout the world," said Smith. "If he did not take letters out and mail them then they would see to it that his family suffered the consequences."

Flashbacks and depression

When he returned to the US he was suffering from panic attacks, insomnia, nightmares, flashbacks and depression.

Another guard whom Smith treated described an incident in which a prisoner had hanged himself in his cell after partially gnawing his own arm off. The prisoner lost a substantial amount of blood but was cut down by guards and survived.

Amnesty International UK spokesperson Neil Durkin pointed out that the psychological trauma inflicted on the Guantánamo inmates should not be overlooked. "With numerous suicide attempts and reports of Guantánamo prisoners on the edge of psychosis, we are extremely concerned that even those eventually released from the camp will be mentally scarred for the rest of their lives," he said. "Over 200 of the Guantánamo prisoners are now held in solitary confinement - and after years of detention without charge or trial this is taking a heavy toll."

There have been few scientific studies of the psychological effects of working as a prison guard, but classic experiments in the 1960s and 1970s showed how easy it is to prompt ordinary people to perpetrate extremely cruel acts given the right conditions.

In the so-called 'Stanford prison experiment' in 1971, college students were asked to act out roles as guards and detainees in a mock prison in the basement of the university's psychology department. Both groups quickly adapted to their roles and the guards became increasingly sadistic and cruel in their treatment of the prisoners. The results were so shocking the experiment was stopped early.

"It's not that we put bad apples in a good barrel. We put good apples in a bad barrel. The barrel corrupts anything that it touches," the experiment's author Dr Philip Zimbardo is quoted as saying on the American Psychological Association's website.

· This article was amended on Tuesday February 26 2008.