Lena Dunham Spills on Snorting Lactose Lines for Wild 'Girls' Scene

Lactose lines and zero regrets -- that’s how Lena Dunham is spilling the tea on one of the most chaotic "Girls" scenes.

Dunham shared the behind-the-scenes chaos this week on the "Las Culturistas" podcast with Matt Rogers and Bowen Yang -- revealing the show’s infamous Season 2 “cocaine” scene with Andrew Rannells was actually powered by lactose powder … not drugs.

Watch the clip ... Dunham says the duo snorted lactose powder take after take while filming the bathroom bender ... and yeah, it was as gross as it sounds.

"We snorted tons of milk off a toilet that day," she said.

But here’s where it gets wild ... the shoot dragged deep into the night, with the cast rolling into a club scene around 5 AM and still going strong by 7:30 AM. By then, they were sweaty, delirious, and riding a bizarre combo of exhaustion and dairy dust.

Dunham admits they had no clue what snorting milk powder would actually do to their bodies -- and spoiler: it wasn’t great. Think sinus chaos, general misery … the whole nine.

Still, that unhinged energy translated perfectly on screen. The jittery, slightly unwell vibe fans clocked as “coked up” was actually just two actors running on fumes and lactose.

And the timing of the reveal isn’t random. Dunham’s been revisiting her "Girls" days lately -- and not always fondly. She recently called out former co-star Adam Driver, alleging he had explosive on-set tantrums, including screaming in her face and damaging property.