The actress, who celebrated her 18th birthday on Tuesday with a party on the beach, is the latest mustachioed face of those "Got Milk?" ads.
"You don't have to be a hero to feel invincible. That's why I drink milk," she says in the ads, part of a campaign to get teens to drink three glasses of low-fat or fat-free milk a day.
The ads, debuting Sept. 10, were shot in May by famed photographer Annie Leibovitz and show Panettiere in a sleek red dress holding an exploding glass of milk.
On Monday, the actress joked to David Letterman on his Late Show about her milestone birthday: "I don't think much changes when you're 18 – maybe the way people treat you. But I think the only things I can do is buy cigarettes, porn and, if I get in trouble with the law, I'm kind of screwed."
Check out behind-the-scenes video of Panettiere's photo shoot: