Modafinil
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GradeResponse
GradeResponse
Modafinil
Class: Wakefulness-promoting agent (eugeroic) | Schedule: FDA Schedule IV controlled substance
Mechanism of Action
Modafinil's exact mechanism is not fully understood. It modulates multiple neurotransmitter systems:
- Dopamine, serotonin, norepinephrine reuptake inhibition
- Histamine signaling enhancement
- Hypocretin (orexin) system activation
- Glutamatergic circuit activation
- GABA inhibition
This combination promotes wakefulness distinctly from classical stimulants (amphetamines), with a lower abuse potential.
(Management of Stimulant Use Disorder, p. 62)
FDA-Approved Indications
| Indication | Notes |
|---|---|
| Narcolepsy | First-line wakefulness agent |
| Obstructive sleep apnea (OSA) | Adjunct to CPAP for residual sleepiness |
| Shift work sleep disorder | Taken ~1 hour before the shift |
Dosing
| Indication | Typical Dose |
|---|---|
| Narcolepsy / OSA | 200 mg orally once daily in the morning |
| Shift work disorder | 200 mg ~1 hour before shift |
| Range | 100–400 mg/day |
(Dose adjustment may be needed in hepatic impairment; use with caution in the elderly.)
Adverse Effects
- Common: Headache, nausea, nervousness, insomnia, dizziness, rhinitis
- Cardiovascular: Mild increases in heart rate and blood pressure
- Serious/Rare:
- Severe rash (including Stevens-Johnson syndrome, toxic epidermal necrolysis)
- Angioedema, anaphylaxis
- Multi-organ hypersensitivity reactions
- Psychiatric symptoms (anxiety, agitation, mania, psychosis — particularly in predisposed individuals)
Contraindications & Warnings
- Pregnancy: Classified as potentially harmful — a 2018 U.S. registry report showed a higher rate of major congenital anomalies in in utero-exposed children. Use should generally be avoided in pregnancy.
- Oral contraceptives: Modafinil is a CYP3A4 inducer and can reduce contraceptive efficacy — alternative or backup contraception is recommended during use and for ~1 month after discontinuation.
- History of serious rash from modafinil/armodafinil: contraindicated.
(Treatment of Central Disorders of Hypersomnolence, p. 10)
Drug Interactions (Key)
| Interaction | Mechanism | Clinical Implication |
|---|---|---|
| Oral contraceptives | CYP3A4 induction | Reduced efficacy; use backup contraception |
| Cyclosporine | CYP3A4 induction | Reduced cyclosporine levels |
| Warfarin | CYP2C9 inhibition | Monitor INR |
| CYP2C19 substrates (e.g., omeprazole, diazepam, phenytoin) | CYP2C19 inhibition | Elevated substrate levels |
Off-Label Uses (Evidence-Supported)
- Cognitive enhancement / fatigue in multiple sclerosis
- Cancer-related fatigue
- ADHD (second/third-line)
- Cocaine use disorder (studied; modest evidence per Management of Stimulant Use Disorder, p. 62)
- Bipolar depression (adjunctive; requires caution re: mood switching)
- Shift work / jet lag beyond formal diagnosis
Abuse Potential
Classified Schedule IV due to potential for dependence, though its abuse potential is considered lower than traditional stimulants. Euphoric effects are weaker, but misuse for cognitive enhancement is well-documented.
Note: Armodafinil (R-enantiomer) is a related compound with a longer half-life (~15 hrs vs. ~12 hrs for modafinil), allowing once-daily dosing with potentially smoother wakefulness throughout the day.
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