Shaun got candid about his addiction at the Mic Drop Comedy Club in San Diego this month, taking incredibly serious source material and turning it into stand-up ammo.

He got the crowd laughing pretty hard by poking fun at his own mugshot from his 2020 arrest. He dives deep into his struggles with substance abuse -- with some wit of course -- and gets a roar of applause when he announces he's now 3 years sober.

Check out his last bit about what his "triggers" are for wanting to use drugs. Again, he's probably not joking ... yet he finds a way to crack up the crowd.

Shaun, who played Goldberg in 'Ducks,' has been working on his stand-up act for a little over a year. He's currently on the road and says, "100% of the proceeds go toward helping a child actor stay off drugs."

As we reported, the former child star opened for fellow comedian Russell Peters at a show last year ... following his time living on the streets and having several run-ins with the law.

BTW, Shaun tells us he was recently hired by the treatment center where he used to be a patient to be a sober coach and interventionalist.

He's looking to jump-start a program that helps people turn their personal trauma into comedic material, just like he's doing.