Modalert (modafinil) lasts 8–12 hours, depending on a person’s metabolism, dose, and general health. Peak blood levels typically occur two to four hours after administration, and the effects progressively diminish. For people who suffer from narcolepsy, shift work sleep disorder, or exhaustion from sleep apnea, Modalert’s extended duration makes it an excellent medication for fostering prolonged alertness and focus throughout the day. It is less likely to cause crashes or withdrawal symptoms than typical stimulants because of its gentler onset and offset. But if you take it too late in the day, it can disrupt your sleep at night. Always heed medical advice to ensure safe usage.