The former child star was ordered to undergo 90 days of in-patient treatment for her substance-abuse issues and probation violations related to drunken driving and theft cases.
She is scheduled to begin rehab May 2 at Seafield Center, Westhampton Beach, N.Y., a facility that allows patients to take drugs prescribed by a doctor, but not Adderall, TMZ reported.
Adderall -- a psychostimulant containing amphetamine -- is prescribed to treat ADHD, though many people abuse it for weight-loss reasons and to get high, the celebrity news website said.
Lohan has used the prescription drug for years and sources said she told friends if the facility tries to wean her off it, she won't stay for treatment. She said she's tried other medications and Adderall is the only one that works for her, TMZ reported.