 Monkeys will self-administer modafinil if they have previously been trained to self-administer cocaine.As such, modafinil is classified by the United States FDA as a schedule IV controlled substance, a category for drugs with valid medical uses and low but significant addiction potential.Large-scale clinical studies have found no evidence of tolerance with modafinil at therapeutic dosages even with prolonged use (for 40 weeks and as long as three years).