Using more than four tablets per day can lead to an overdose. This compound is responsible for many activities in the brain, one of which is the process of learning and memory. Orexin is responsible for regulating the waking portion of our "sleep-wake cycle". The dosage strength will vary depending on persons. This eugeroic drug is specifically prescribed for narcolepsy and obstructive-sleep apnea. It is not known how modafinil works to keep you awake. It increases the neurotransmitters associated with the sensation of wakefulness, including dopamine, norepinephrine, and histamine. That said, there are many reports online of people feeling high from modafinil. It's percentage is growing among sleep disorders and, according to some researches, is approaching 30%. People who take modafinil, are trying to stay awake longer. As a general rule of thumb, modafinil is considered a prescription-only medication. This Provigil pill has proved its efficacy in treating the obstructive sleep apnea (OSA) and shift work disorder (SWD) and also for the treatment of narcolepsy. The drug is strictly prohibited for patients with cirrhosis and severe liver diseases.