Lindsay Lohan's skin and bones physique is the result of taking Adderall, it's claimed.

The prescription drug is normally used to treat deficit hyperactivity disorder but weight loss can be a side affect.

"She takes Adderall all the time," a source tells Us magazine. "She gets jittery because of the way the pills affect her.

"It's a major reason why she's losing weight."

But despite flaunting a scarily skinny frame as she frolicked in a bikini during her recent Hawaiian mini-break with her family, Lindsay insists she's healthy.

"I've been eating enough," she tells E! News.

"We're a tight family. We've been through a lot so we take care of each other...We went hiking and everything in Maui, so it was really good."

See Lindsay's skinny dip below