Modafinil

Overview

Modafinil is a wakefulness-promoting agent (eugeroic) used primarily for sleep-related disorders. It is classified as a Schedule IV controlled substance in the US.

Mechanism of Action

The exact mechanism is not fully understood, but modafinil modulates multiple neurotransmitter systems:

Dopamine, serotonin, norepinephrine reuptake inhibition
Histamine and hypocretin (orexin) signaling activation
Glutamatergic circuit activation
GABA inhibition

Unlike amphetamines, it does not cause significant dopamine release, which accounts for its lower abuse potential (Management of Stimulant Use Disorder, p. 62).

Approved Indications

Indication	Notes
Narcolepsy	First-line wake-promoting agent
Obstructive sleep apnea (OSA)	Residual sleepiness despite CPAP
Shift work sleep disorder	Taken ~1 hour before shift

Dosing

Standard dose: 200–400 mg each morning (Harrison's, p. 909)
Taken as a single morning dose for narcolepsy/OSA
For shift work disorder: taken ~1 hour before the work shift
Available in 100 mg and 200 mg tablets

Comparison to Other Wake-Promoting Agents

Drug	Mechanism	Abuse Potential	Notes
Modafinil	Multi-neurotransmitter	Lower (Schedule IV)	Fewer sympathomimetic side effects
Methylphenidate	NE/DA reuptake inhibitor	Moderate (Schedule II)	10–20 mg BID
Dextroamphetamine	DA/NE release + reuptake	Higher (Schedule II)	10 mg BID
Solriamfetol	NE/DA reuptake inhibitor	Moderate (Schedule IV)	75–150 mg daily
Pitolisant	H3 receptor antagonist	Low	Non-scheduled

(Harrison's, p. 909)

Pharmacokinetics

Half-life: ~15 hours (allows once-daily dosing)
Metabolism: Hepatic (CYP3A4/5 substrate)
Protein binding: ~60%
Onset: Within 2–4 hours

Side Effects

Common:

Headache (most frequent)
Nausea
Nervousness / anxiety
Insomnia (if taken too late in the day)
Decreased appetite

Serious (rare):

Stevens-Johnson Syndrome / serious rash (black box warning)
Hypersensitivity reactions (angioedema, anaphylaxis)
Psychiatric symptoms (mania, hallucinations, suicidal ideation) in predisposed individuals

Drug Interactions

Reduces efficacy of hormonal contraceptives (CYP3A4 induction) — alternative contraception required
Increased levels of CYP2C19 substrates (e.g., warfarin, phenytoin, diazepam) — monitor closely
CNS stimulants: additive effects

Contraindications & Cautions

Known hypersensitivity to modafinil or armodafinil
History of serious rash with prior modafinil use
Use with caution in patients with: cardiovascular disease, left ventricular hypertrophy, mitral valve prolapse, history of psychosis or mania, hepatic impairment (reduce dose by 50%)

Off-Label Uses

Cognitive enhancement (used as a "nootropic," though evidence for healthy individuals is modest)
ADHD (limited evidence vs. first-line agents)
Cancer-related fatigue
Adjunct in cocaine use disorder (studied as a potential treatment given its dopaminergic modulation)
Multiple sclerosis fatigue

Key Clinical Pearls

Preferred over amphetamines in narcolepsy due to fewer side effects and lower abuse potential (Harrison's, p. 909)
Does not replace CPAP in OSA — it addresses residual sleepiness only
Armodafinil (R-enantiomer) has a longer effective duration and is dosed at 150–250 mg
Patients should maintain good sleep hygiene alongside pharmacotherapy

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