A SOLDIER WATCHES a drab cluster of buildings by the side of a bomb-cratered highway. Inside, the enemy is encamped among civilians. Local farmers and their families are forced to share their basements and shacks, acting as human shields for troops and weapons that threaten the lives of other civilians, the soldier’s comrades and his cause in this messy 21st-century war.

There can be no surgical strikes tonight. The artillery this soldier has the power to unleash will bring flames and screaming. The ground around him will be littered with the broken bodies of women and children, and he will have to walk right through them. Every value he learnt as a boy tells him to back down, to return to base and find another way of routing the enemy.

Or, he reasons, he could take the first, bloody option — then swallow a few pills that, over the next two weeks, will immunise him against a lifetime of crushing remorse.

He draws one last clean breath, and fires.

The prospect of a soul absolved by medication is about to become real. Feelings of guilt and regret travel neural pathways in a manner that mimics the tracings of ingrained fear, so a prophylactic against one could guard against the other. Researchers in the United States and France are working along those lines with some success.

At the University of California at Irvine, experiments on rats indicate that the brain’s hormonal reactions to fear can be inhibited, softening the formation of memories and the emotions they evoke. At New York University researchers are mastering the means of short-circuiting the very wiring of primal fear. At Columbia University one Nobel laureate’s lab has discovered the gene behind a fear-inhibiting protein, uncovering the traditional “fight or flight” imperative at a molecular level. In Puerto Rico, at the Ponce School of Medicine, scientists are discovering ways to help the brain unlearn fear and inhibitions by stimulating it with magnets.

And at Harvard University, survivors of car accidents are already taking the betablocker propranolol in the first human trials of the common cardiac drug’s ability to nip the effects of trauma in the bud. Similar trials are being carried out at the Society for Biological Psychiatry in France.

The web of your worst nightmares, your hauntings and panics and shame, radiates from a dense knot of neurons called the amygdala. With each new frightening or humiliating experience, or even the reliving of an old one, this fear centre triggers a release of hormones that sear horrifying impressions on to your brain. That which is unbearable becomes unforgettable too. Unless, it seems, you act quickly enough to block traumatic memories from taking a stranglehold. Sceptics say that in the name of human decency there are some things people should have to live with. They object to the idea of medicating away one’s conscience. “It’s the morning-after pill for just about anything that produces regret, remorse, pain or guilt,” says Dr Leon Kass, chairman of the US President’s Council on Bioethics. Barry Romo, a national co-ordinator for Vietnam Veterans Against the War, is even more blunt. “That’s the devil pill,” he says. “That’s the monster pill, the anti-morality pill. That’s the pill that can make men and women do anything and think they can get away with it. Even if it doesn’t work, what’s scary is that a young soldier could believe it will.”

The psychiatrist Edmund G. Howe, director of the medical ethics programme at the Uniformed Services University of the Health Sciences in Maryland, agrees. “If you have the pill, it certainly increases the temptation for the soldier to lower the standard for taking lethal action, if he thinks he’ll be numbed to the personal risk of consequences. We don’t want soldiers saying, willy-nilly, ‘Screw it. I can take my pill and even if doing this is not really warranted, I’ll be OK’,” he says.

The scientists behind this advance into the shadows of memory and fear don’t dream of creating morally anesthetised squaddies. They’re trying to fend off post-traumatic stress disorder, or PTSD, so that women who have been raped can leave their homes without feeling like targets; so that survivors of terrorist attacks can function, raise families, and move forward; and yes, so that those young soldiers aren’t left shattered for decades by their experiences.

But if the pill can soothe trauma victims, it can do the same just as successfully for perpetrators. Imagine a world where killers, adulterers and even traitors could smother their remorse at will. Or, worse, use the pill as an aid to their crimes. After all, since betablockers inhibit the reception of adrenalin, people who take them would lack the full “fight or flight” response. That may be bad for soldiers, but could prove a great advantage to, for instance, a hitman who would appreciate the potential for cool detachment.

For doctors, the drugs would present a tricky dilemma. Researchers say that for the medicines to be effective, patients would need to take them soon after the upsetting event. The temptation for physicians might be to err on the side of caution, at the cost of curbing normal emotional responses. Victims might be eager to avoid lasting pain, wrongdoers the full sting of self-examination.

“The impulse is to help people to not fall apart. You don’t want to condemn that,” says Kass. “But that you would treat these things with equanimity, the horrible things of the world, so that they don’t disturb you . . . you’d cease to be a human being.”