Modafinil is a non-amphetamine central nervous system (CNS) stimulant with wakefulness-promoting properties. It is used in the treatment of conditions which cause excessive daytime sleepiness. In the United States, modafinil is FDA-approved for the treatment of the following in adults:

• Narcolepsy: First-line treatment; Modafinil is used to treat the daytime fatigue associated with narcolepsy, and it has not been shown to improve symptoms of cataplexy.
• Sleep Work Shift Disorder: First-line treatment
• Obstructive sleep apnea: Adjunct to continuous positive airway pressure (CPAP)

Additionally, modafinil has reported efficacy for the following “off-label” indications:

• Attention-deficit hyperactivity disorder[1][2]: Some evidence of efficacy exists in the pediatric population. A recent study of adult ADHD patients found no benefit of modafinil.[3]
• Acute unipolar and bipolar depressive episodes[4]
• Cocaine dependence: Evidence regarding the efficacy of modafinil for this purpose appears mixed[5][6]
• Cancer-related fatigue: Evidence regarding the efficacy of modafinil for this use appears mixed.[7][8]
• Multiple sclerosis-related fatigue[9]

The use of modafinil as a “cognitive enhancer” in healthy subjects has been suggested in the literature; however, the precise benefits and risks associated with this use remain uncertain.[10][11]

Modafinil is known to be a weak inhibitor of dopamine reuptake, which may be its primary clinically important property. It has little to no in vivo affinity for the serotonin (5HT) or norepinephrine (NE) transporters, although elevated concentrations of NE and 5HT in the prefrontal cortex and hypothalamus have been observed following modafinil administration, possibly as an indirect effect of increased extracellular dopamine.[12] Additionally, modafinil has been postulated to increase signaling in the hypothalamic orexin and histamine neurotransmitter pathways,[13] and animal studies have also suggested a glutamatergic effect.[14] A potential advantage of modafinil is its very low observed propensity for causing euphoric effects associated with traditional psychostimulants (e.g., cocaine, amphetamine). This has been attributed to differences in its interaction with the dopamine transporter at the molecular level.[15] In several laboratory studies of healthy subjects, modafinil has also been shown to reduce the euphoric effects of cocaine.[16][17]

Modafinil exists as a racemic mixture of S- and R-enantiomers. Of note, the R-enantiomer is thought to be the source of modafinil’s psychotropic properties and is marketed independently as armodafinil.

Modafinil is available exclusively in the form of oral tablets; the usual dose is 200mg once daily. It is insoluble in aqueous solution and therefore cannot be administered intravenously. The elimination half-life of a single dose in healthy subjects is approximately 15 hours.[18] Maximum plasma concentration is reached 2-4 hours after administration. Modafinil undergoes hepatic metabolism via multiple pathways, including CYP3A4. 80% of the dose is recovered in the urine in the form of metabolites. Severe renal and/or hepatic impairment are known to cause significantly increased steady-state drug concentrations. Dose reduction is recommended in patients with severe hepatic impairment.

Modafinil is generally well-tolerated stimulant. The most commonly reported adverse effects of modafinil (less than 10% of users) are a headache, nausea, and decreased appetite. Other commonly reported adverse effects (5% to 10% of users) include anxiety, insomnia, dizziness, diarrhea, and rhinitis.

Regarding serious adverse effects, cases of Stevens-Johnson syndrome, toxic epidermal necrolysis, and drug rash with eosinophilia and systemic symptoms (DRESS) have been reported in postmarketing surveillance. These life-threatening rashes associated with modafinil appear to be extremely rare, although the precise incidence rates are not known. Most of the reported cases have occurred within six weeks of drug initiation. Therefore, any patient who develops a rash during this time frame is advised to notify the prescribing physician immediately.

There are few, if any, absolute contraindications to the use of modafinil. The following is a list of relative contraindications, cautions, and special considerations: 

• Cardiovascular disease: Modafinil is not recommended in patients with documented left-ventricular hypertrophy or with a history of previous cardiotoxicity related to psychostimulant use. It should be used with caution in patients with uncontrolled hypertension, unstable angina, or recent myocardial infarction.
• Hepatic impairment: Dose reduction to a maximum of 100mg daily is recommended in patients with severe hepatic impairment.
• Renal impairment: Modafinil should be used with caution in patients with severe renal impairment. However, no recommendations for renal dosing exist.
• Psychiatric disorders: Modafinil should be used with caution in patients with a history of psychosis and/or mania. Such patients should be monitored for hallucinations, delusions, mania, aggression, and suicidal ideation upon starting modafinil. Discontinuation is advised if these symptoms develop.
• Tic disorders: Limited evidence suggests that all CNS stimulants may exacerbate tics in patients with pre-existing tic disorders. A baseline assessment of tics is recommended prior to initiating treatment.
• Pregnancy: There is no evidence to suggest or exclude harm to the human fetus associated with modafinil. However, an increased risk of abortion and intrauterine growth restriction has been observed in some animal studies. Risks and benefits of therapy during pregnancy should be carefully considered.
• Lactating women: It is unknown if modafinil is excreted in breast milk.