A stress-blocking drug can be used as a "compassion pill" that increases empathy, the ability to feel another's pain.
That's according to a new study, which has also provided the first evidence that stress can sap the caring instincts of humans - which possibly helps to explain acts of cruelty committed in the heat of conflict.
Scientists have found that stress undermines empathy, both in laboratory mice and volunteer students taking part in experiments that involved friends or strangers immersing their hands in freezing cold water.
In both cases, treatment with the stress-hormone-blocking drug metyrapone reduced the effect and increased the ability to empathise.
Metyrapone is a pill commonly used to treat Cushing's syndrome, a condition that causes the body to produce excess levels of the stress hormone cortisol.
A similar result was achieved in the human study.
Study leader Dr Jeffrey Mogil, from McGill University in Canada, said: "We found what in some sense might be thought of as the 'secret' to empathy; that is, what prevents it from occurring more often between strangers."
Previous research by the same team has demonstrated that mice experience empathy - once thought to be a wholly human ability - but only when they are known to each other.
Two cage-mates given a painful experience will feel it more than when each of them undergoes the same experience alone.
In the new study, published in the journal Current Biology, mice were subjected to mild pain by injecting them with acetic acid.
As before, cage-mates - but not strangers - who suffered the same experience together showed a greater reaction than they did when injected alone.
When they were treated with metyrapone, the mice began showing the same level of empathy to strangers as they did to their cage-mates. This suggested it was the stress of being with a stranger that previously inhibited their empathy.
A similar response was seen in the undergraduate volunteers.
When friends were paired together and told to hold their hands in iced water, they reported a greater sensation of pain than individuals on their own or two strangers undergoing the same experience.
Treatment with metyrapone caused students to feel more empathy for people they viewed as strangers.