Narcolepsy is a sleep disorder that causes excess sleepiness. Recently, a study has shown that narcolepsy may be associated with low levels of a compound called carnitine, which is involved in fatty acid metabolism. This study looked at the effects of supplementing L-carnitine in 28 patients with narcolepsy. The study was a randomized, double-blinded, cross-over, and placebo-controlled design that lasted 16 weeks. The participants took 340 mg of L-carnitine in the morning and 170 mg of L-carnitine in the evening. The participants were allowed to take traditional medications for narcolepsy. The primary outcome measure was the patient's subjective assessment of their sleepiness, which was based on the total time the person reported they dozed off during the daytime as recorded in their sleep logs. Of note, there was no objective measurement of sleepiness, such a multiple sleep latency test.
Results showed a statistically significant reduction in subjective dozing time when participants took L-carnitine. Specifically, participants dozed for 49 +/- 34 minutes / day on L-carnitine versus 58 +/- minutes per day on placebo. This may be statistically significant, but I wonder how clinically significant it is. Researchers reported no side effects to the L-carnitine.
The researchers also noted that low carnitine levels may be seen in chronic fatigue syndrome, and that it's been reported that L-carnitine supplementation resulted in significant improvement in fatigue severity after two months of use.