‘That Laugh Is a Drug.’ HBO’s New Documentary Explores Robin Williams’ Relationship to Comedy and Addiction

Substance use loomed large over Robin Williams’ life. But a lesser-known addiction of the late entertainer may have been comedy itself, suggests HBO’s new documentary Robin Williams: Come Inside My Mind.

Come Inside My Mind, directed by Marina Zenovich, offers a two-hour glimpse into Williams’ psyche through audio clips, archival footage and interviews with his friends and family. In doing so, it paints a vivid picture of the extent to which Williams, who died by suicide in August 2014, devoted his 63 years of life to making others laugh.

Williams describes the passion he felt for comedy almost as a compulsion. “There’s a real incredible rush, I think, when you find something new and spontaneous,” Williams says in an interview excerpted in the film. “I think your brain rewards that with a little bit of endorphins — going, ‘If you think again, I’ll get you high one more time.’”

Williams — who by all accounts could go from zero to 60 in seconds, flipping a switch from quiet and pensive at home to a ball of energy on stage — became known for that need. “The urge to be funny, and to make people laugh, was so innate for him. It was almost like breathing for him,” Mark Romanek, who directed Williams in One Hour Photo, said in an interview in Come Inside My Mind. “When he used to make people laugh that hard, he used to kind of get high from it.”

Fellow comedian and close friend Billy Crystal added that Williams, who publicly struggled with alcoholism and drug use, grew to depend on the rush that laughter provided. “He needed that little extra hug you can only get from strangers,” Crystal said in the film. “That laugh is a drug. That acceptance. That thrill is really hard to replace with anything else.”

Positive social interactions, like making people laugh, do trigger the endogenous opioid system, the body’s natural pain-relieving mechanism, Dr. Nora Volkow, the director of the National Institute on Drug Abuse and one of the leading researchers on addiction neurology, tells TIME. The brain response is less intense, but not dissimilar, from that triggered by drugs like heroin, she says.

“That’s why social interactions are so pleasurable: They are associated with activation of the endogenous opioid system,” Volkow explains. (The documentary’s oft-mentioned endorphin hit probably isn’t as much of a factor as endogenous opioids, Volkow says, though the hormone oxytocin, which makes us feel closer to others, might play a role.) “Something like heroin is rewarding because it’s [also] activating that endogenous opioid signaling system. It’s a very pleasurable system. It is there to make us feel good about behaviors in such a way that we will repeat them.”

So while it’s unlikely that someone would be truly addicted to laughter, at least in a clinical sense — “If it were a real addiction, it would mean that you were not able to do anything else; it would be at the expense of your own wellbeing,” Volkow says — it’s perfectly feasible that someone could become dependent on that feeling. Humans, after all, are social creatures; interaction activates our pleasure circuits because it’s in our nature to find groups and partners.

“Because social interactions make you feel so good, when they are no longer there, you feel uncomfortable. You seek them out because you feel you need them in order to feel good,” Volkow says. “That may become one of the main sources of pleasure that you get, and if you don’t get it, then of course you miss it and you feel like something is lacking.”

Somebody like Williams, who struggled with addiction, could be especially susceptible to that effect, Volkow says. “If you have a personality that’s prone for addictive behaviors, which basically means that you’re conditioned rapidly and you impulsively repeat those behaviors, then you could see that you get conditioned faster to a situation that’s rewarding, like having the social recognition that your jokes are very funny,” she explains. “That’s highly rewarding and reinforcing. It can start to become pathological.”

The documentary suggests that that may have been the case for Williams. And though that tendency propelled Williams and his comedy to fame and millions of adoring fans, it also cast a dark shadow at times.

“His pathos was to entertain and to please,” Williams’ son Zachary says in the film. “And he felt that when he wasn’t doing that, he was not succeeding as a person. That was always hard to see, because in so many senses, he was the most successful person I know. And yet he didn’t always feel that.”

Come Inside My Mind premieres on HBO Monday, July 16, at 8 p.m. ET.