OSU6162 is a drug developed by Professor Arvid Carlsson. The pharmacological action has been characterized as dopamine and serotonin stabilizing with beneficial effects in neuropsychiatric diseases. OSU6162 has also been shown to be virtually side effect free. In relatively recent treatment trials, it was somewhat surprisingly observed that the preparation had a significant and positive clinical effect on mental fatigue. In a double-blind cross-over study in twelve patients with mental fatigue triggered by stroke or traumatic brain injury, a significant effect was seen, which in some patients was quite dramatic. Extended open-label clinical trials to study the safety and long-term efficacy of OSU6162 are now planned. Optimal dosing of the drug and its side effect profile will also be further studied. These studies may include patients with different diagnoses, previously studied in placebo-controlled trials with OSU6162. There are theoretical reasons for assuming that OSU6162 can counteract various symptoms of narcolepsy and thus replace the currently dominant but problematic central stimulants. Twelve patients with narcolepsy are planned to be included in a randomized double-blind cross-over comparison with placebo. Efficacy will be assessed using rating scales and self-reporting of symptoms.