Nicole on Adderall

Insiders reported that Nicole Richie has been using Adderall - a prescription drug normally used to treat Attention Deficit Hyperactivity Disorder and is a powerful appetite suppressant.

"She loves Adderall because she stays awake, and it makes her not want to eat," says a close pal. "And she takes it even more when she's filming."

Although her rep denies that she uses the drug, a pal says Nicole's actually increased her dosage: "She's taking more and more lately."