This study will last 16 weeks. Participants will be randomly assigned to one of four groups: 1) 60 mg dose of d-amphetamine; 2) 400 mg dose of modafinil; 3) 30 mg dose of d-amphetamine combined with 200 mg dose of modafinil; and 4) placebo. All participants will receive 200 mg of modafinil over 4 days.