The effects of Modalert 200 (modafinil) usually appear 30 to 60 minutes after consumption. Approximately two to four hours after consuming it, its blood levels peak. The effects, which assist sustain attention and alertness throughout the day or shift, can last anywhere from 10 to 12 hours. However, a person's metabolism, body weight, and whether or not they take it with meals can all affect how quickly they respond. For optimal effects, it is advised to adhere to your physician's recommendations on dose and time. Avoid taking it too late in the day at all times to avoid disturbing your sleep.