Alongside painkillers, food, and technology, one psychiatrist worries about the addictive potential of getting back at people — or even thinking about it.

James Kimmel knows the danger well.

Now a psychiatrist at the Yale School of Medicine, he once was moments from being a teenage murderer. In a lecture given Wednesday, Kimmel explained how he wielded a loaded gun against school bullies after years of worsening torment — and why he didn’t fire.

“At the last second, I had this split second of insight,” Kimmel told his audience at the remote Community Conversations event hosted by the Harvard Graduate School of Design. “If I went ahead with this, I’d have, for the rest of my life, to identify as a murderer — and that was not an identity that was acceptable to me.”

It was just enough time to break the spell of “sweet revenge” — a psychological phenomenon that, Kimmel argued, works very much like any other drug.

When people are harboring a grievance, no matter its validity, Kimmel said, “It’s a very real pain. And your brain really, really doesn’t want pain — and so it instantly scrambles to rebalance that pain with pleasure.”

Decades of functional MRI data show the result: As subjects fantasize about settling scores, the brain’s reward and pleasure centers flood with dopamine — just as they would from gambling or tobacco.

And, just as with gambling or tobacco, the high doesn’t last. “It spurs us to go further, fantasize even more heavily, or go and take a physical act of revenge — to get that hit again and again,” Kimmel said.

Viewed from outside, the psychological cycle of resentment and revenge has an obvious grim futility. And yet in population studies, almost 100 percent of subjects will confess to having had at least one revenge fantasy in their lives.

“It’s thought to be part of an adaptive strategy from the Ice Age: to stop people from stealing your mate, stealing the food you need for the coming winter,” Kimmel said. “But now, of course, we seek revenge for threats that are just to our egos, that don’t have life-or-death consequences.”

If revenge is a cheap thrill, Kimmel argued, “Forgiveness is something of a wonder drug.” 

Kimmel argued that the ancient brain chemistry lies at the root of most contemporary conflict, from ongoing wars and rancorous political divisions to social media spats.

What has changed, he said, is the technology: Notably, algorithms that have learned to exploit the druglike potential of contesting with an enemy.

“Now, when political leaders express a grievance, they can instantly ‘infect’ millions of people with that same grievance,” Kimmel said.

Online platforms don’t just act as vectors for rapid spread. They also offer a means of instant relief: to “fire back” violent or cruel rhetoric at the perceived enemy.

For that reason, Kimmel believes those algorithms should be regulated just as if they were herbicides or pesticides — hazardous to human health.

But he does also see avenues for hope.

Looking back at his harrowing teenage experience, Kimmel sees that moment of insight as having given his prefrontal cortex — momentarily swamped by the operation of rage in other parts of the brain — a chance to recover and do its protective work.

And near-misses are common: While revenge fantasies are nearly universal experiences, only about one in five say they have acted on those fantasies.

What’s more, once we come to see revenge in his terms, Kimmel said, we gain tools against it: namely, cognitive-behavioral therapy, peer-support programs like Alcoholics Anonymous, and — potentially — GLP-1 drugs that have shown promise in reducing other kinds of cravings.

In a book published this spring and a free app, Kimmel offers his own intervention: a kind of imaginary courtroom where perceived wrongs can be considered, judged, and — eventually — released.

If revenge is a cheap thrill, Kimmel argued, “Forgiveness is something of a wonder drug.” The same brain scans show that after a harm, forgiveness “actually deactivates the anterior insula, the pain network inside your head. So instead of covering it up with a dopamine rush, you’re actually getting pain stoppage.”

Easier said than done, of course. Kimmel calls his imaginary courtroom the “non-justice system” for a reason — it aims not to settle accounts but to offer liberation from a destructive pattern.

After hearing both sides and weighing a sentence, “In the final judgment, you’re given an opportunity to imagine what it would feel like if you decided to forgive — you don’t even have to commit” to going that route, Kimmel said.

Even at the notion of breaking the cycle, Kimmel said, participants report they feel an instantaneous sense of relief — evidence that, despite its pleasures, “revenge-seeking is hard work.”