Modafinil

Modafinil (sold under the brand names Alertec, Alertex, Altasomil, Aspendos, Forcilin, Intensit, Mentix, Modafinil, Modafinilo, Modalert, Modanil, Modasomil, Modvigil, Modiodal, Modiwake, Movigil, Provigil, Resotyl, Stavigile, Vigia, Vigicer, Vigil, Vigimax, Wakelert and Zalux among others) was was originally developed in France by professor Michel Jouvet and Lafon Laboratories (1970s).

In many countries it is currently a prescription-only medication, and is used to treat sleepiness due to narcolepsy, shift-work sleep disorder, or obstructive sleep apnea. There are ongoing clinical trials for its use in fatigue, cocaine addiction, Attention-Deficit / Hyperactivity Disorder (ADHD)plugin-autotooltip__plain plugin-autotooltip_bigAttention-Deficit / Hyperactivity Disorder (ADHD)

Attention Deficit Hyperactivity Disorder (ADHD) is a neuro-developmental mental disorder. It's characterized by problems in paying attention, excessive activity, or difficulty in controlling behavior (typically not appropriate for a person's age). Symptoms usually begin at between six to twelve years of age, and, to be classified as ADHD must be present for more than six months and cause problems in at least two settings (e.g. school, home, or i…
, Major Depressive Disorderplugin-autotooltip__plain plugin-autotooltip_bigMajor Depressive Disorder

Major Depressive Disorder (MDD), also known simply as 'depression', is a mental disorder characterized by at least two weeks of pervasive low mood.

Current estimates are that severe depression affects around 2% of the global population at any given time, currently more than 150 million. The majority of cases don't appear to have an obvious personal and/or societal cause.
, seasonal affective disorder, bipolar depression, nicotine addiction, and Schizophreniaplugin-autotooltip__plain plugin-autotooltip_bigSchizophrenia

"Schizophrenia is a mental disorder characterized by abnormal social behavior and failure to understand what is real. Common symptoms include false beliefs, unclear or confused thinking, auditory and visual hallucinations, reduced social engagement and emotional expression, and a lack of motivation."
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It's also routinely used by the military to keep operatives awake for long periods - and (unofficially) by shift-workers and students studying for exams etc etc.

Its mechanism(s) of action have been very widely researched, but as yet there is no official consensus on how it works. To the extent that it's been called 'a drug in search of a mechanism'.

See: Mechanisms of modafinil: A review of current research Neuropsychiatric Disease and Treatment. 2007 Jun; 3(3): 349–364.