Modafinil 400 mg is a higher-strength presentation of modafinil, a prescription medicine primarily associated with promoting wakefulness. It is commonly discussed in relation to excessive daytime sleepiness caused by conditions such as narcolepsy, obstructive sleep apnea, and shift work sleep disorder. Modafinil works through effects on several neurotransmitter systems in the brain, helping increase alertness and reduce unwanted sleepiness during waking hours.

The 400 mg amount refers to the total quantity of modafinil taken in a day, rather than indicating a separate active ingredient. In clinical practice, the appropriate dose depends on the condition being treated, individual response, and the prescribing information applicable to the patient. Although 400 mg is sometimes used in clinical settings, higher doses do not necessarily provide proportionally greater wakefulness, so dosage decisions should be based on established medical guidance rather than simply increasing the amount.

Modafinil has a relatively long duration of action, which is one reason timing can be important. Its pharmacological activity can remain present for many hours after administration. The medicine is generally taken according to a specific schedule related to the sleep disorder being treated. For people with shift work sleep disorder, timing may be different from that used for other wakefulness-related conditions.