Fame Pictures snappers photographed the 'Toxic' singer carrying a packet of Provigil, a prescription drug used to treat excessive daytime sleepiness and narcolepsy, in her open purse.
While she was snapped the 25-year old was going to her first co-parenting class with Kevin Federline at the Beverly Hills Hotel.
Dr. Mark Milstein, a New York neurologist said that the traditional stimulant, Provigil cannot be used as a drug and its primary effect was to keep away from falling off to sleep.
"Unlike a traditional stimulant with side effects such as hyperactivity and inattentiveness, the primary effect of this medication is only to help keep you from falling asleep," US magazine quoted him, as saying.
"Somebody who is living a celebrity lifestyle, who frequently has to be up very early one day and then very late the next, could develop very disordered sleep patterns," he said.
"This medication won't give you a 'high,' like a stimulant would," Dr. Milstein added.