5-HTP is a precursor for serotonin which can be further processed into melatonin. Despite this theoretical mechanism for promoting sleep, current research is limited and not particularly promising.
Some early research in the 1970s suggested that 5-HTP might increase REM sleep without affecting total sleep duration, but several participants reported experiencing nightmares.[1][2] Furthermore, a 2022 randomized controlled trial in people with Parkinson’s disease found no effect on REM sleep.[3]
In children with sleep terrors, 5-HTP was reported to significantly reduce night terror episodes, but the study was not placebo-controlled.[4]
In a 2024 study (summarized here), 5-HTP taken before bed for 12 weeks did not improve sleep but rather was reported to slightly decrease sleep duration in older adults.[5]