Modafinil dosage

This page is a reference summary of published evidence and regulatory documents. It is not a substitute for individual medical advice, and it is not a recommendation to take or avoid any medicine.

Medically reviewed by Dr. Sofia Lindqvist, · Last reviewed 11 August 2026

The approved modafinil dose is 200mg once daily, taken in the morning for narcolepsy and obstructive sleep apnea (OSA), or about one hour before a shift for shift work disorder (SWD). Dose adjustments apply in hepatic impairment and older adults, and no dose has been established for off-label use.

Approved doses by indication

Indication	Standard dose	Timing
Narcolepsy	200mg once daily	Morning
Obstructive sleep apnea	200mg once daily	Morning, alongside continued primary OSA treatment
Shift work disorder	200mg once daily	Approximately 1 hour before the start of the shift

These are the doses studied in the pivotal trials supporting FDA approval and are the doses listed on the current label. See the modafinil overview for how the three indications differ.

The 400mg question

400mg once daily is an FDA-approved dose and appears on the label as an option, but trials comparing 200mg and 400mg doses did not consistently show additional benefit at the higher dose. Some prescribers use 400mg when 200mg is not adequately controlling sleepiness, but the evidence for added efficacy at that dose is not strong, and higher doses may increase the likelihood of effects such as headache or nervousness. See modafinil side effects for incidence data.

Hepatic impairment

Modafinil is metabolised primarily by the liver, and clearance is reduced in patients with hepatic impairment. The FDA label recommends halving the dose in patients with severe hepatic impairment — typically to 100mg per day — reflecting reduced drug clearance rather than a change in target effect.

Older adults

Modafinil clearance may be reduced in older adults, and the label recommends considering a lower dose or slower titration in this population, though no specific reduced dose is mandated the way it is for hepatic impairment. Age-related reductions in renal and hepatic function should be taken into account alongside other medications the person is taking; see modafinil interactions.

Missed doses

Because modafinil is typically dosed once daily and has an elimination half-life of around 15 hours, a missed morning dose taken later in the day increases the risk of insomnia that night. If a dose is missed and it is already afternoon or evening, skipping that day’s dose is generally preferable to taking it late. See how long modafinil lasts for the half-life and timing detail behind this.

Dosing for off-label or non-approved use

There is no established dose for off-label or non-medical use of modafinil. Studies investigating cognitive effects in healthy volunteers have used single doses ranging from 100mg to 400mg, but these were research doses chosen for study design purposes, not a validated or recommended regimen. No controlled dose-ranging work has been done to establish a minimum effective or safe dose outside the approved indications, and this page does not provide one. See modafinil and cognitive enhancement for what those studies measured.

Frequently asked questions

What is the standard modafinil dose?

200mg once daily, taken in the morning for narcolepsy and obstructive sleep apnea, or approximately one hour before the start of a shift for shift work disorder.

Is 400mg of modafinil better than 200mg?

Clinical trials comparing 200mg and 400mg doses did not show a consistent additional benefit at 400mg, though it is an FDA-approved dose and some patients are prescribed it.

Does liver impairment change the modafinil dose?

Yes. The FDA label recommends reducing the dose in patients with severe hepatic impairment, typically to 100mg per day, because modafinil clearance is reduced.

What is the dose for off-label or non-medical use?

There is no established dose for off-label or non-medical use. Doses used in cognitive-enhancement research studies have ranged from 100mg to 400mg as a single dose, but this reflects study design, not a recommended regimen.

What should I do if I miss a dose?

Take it as soon as remembered if it is still early in the day; if it is later, skipping the dose is generally preferable to taking it too close to bedtime, since modafinil can disrupt sleep. There is no need to double the next dose.