When Nicole Richie was hospitalized on March 2 for dehydration, one friend worried Nicole was back on heroin, but celeb snitches claim that it’s a prescription that has turned Nic back it an addict.

Insiders say Nicole 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.”