Philip Seymour Hoffman was all smiles at the 2013 Envision Awards in NYC yesterday ... the first major event the actor's attended since leaving detox for narcotic abuse 3 weeks ago.

Hoffman was clutching a bottle as he walked the red carpet ... but fear not, it was just some sparkling water.

We broke the story ... Hoffman entered a detox facility on the East Coast for a 10-day stint back in May ... in an effort to curb a drug problem that was spiraling out of control.

The 45-year-old Oscar winner had struggled with substance abuse in his early 20s -- but kicked the habit for 23 years -- only to fall off the wagon more than a year ago.  PSH told TMZ the problems started with pills and escalated to snorting heroin.

Hoffman got treatment to nip the problem in the bud -- and went back to work on a movie a couple of weeks ago.

FYI -- Hoffman attended the event to honor Michael Barker and Tom Bernard, Co-Presidents and Co-Founders of Sony Pictures Classics (pictured above).