L-tryptophan

noun

L-tryp·​to·​phan ˈel-ˈtrip-tə-ˌfan 

: the levorotatory form of tryptophan that is a precursor of serotonin and was used formerly as a dietary supplement especially to promote sleep and relieve depression

Examples of L-tryptophan in a Sentence

Recent Examples on the Web

Rebalance Dream Sleep Mints (Melatonin-Free; 31-Pack) for $46: These melatonin-free mints are designed to slowly dissolve, with natural sleep-inducing ingredients like L-theanine, L-tryptophan, GABA, and slow-release Reishi mushroom. —Molly Higgins, Wired News, 23 Jan. 2026

Not just another gourmet candy bar, the dark chocolate with lavender and blueberry flavors is infused with the hormone melatonin, the amino acid L-tryptophan, a blend of soothing botanicals and something called PharmaGABA, an artificial version of a neurotransmitter that calms the brain. —Karen Kaplan, Los Angeles Times, 4 Dec. 2024

This could be due to ingredients like ginger or L-tryptophan, which can irritate sensitive stomachs. —Amber Smith, Discover Magazine, 5 Aug. 2023

Word History

First Known Use

1949, in the meaning defined above

Rhymes for L-tryptophan

• tryptophan
• boffin
• coffin
• offen
• often
• soften

Medical Definition

L-tryptophan

noun

L-tryp·​to·​phan ˈel-ˈtrip-tə-ˌfan 

: the levorotatory form of tryptophan that is a precursor of serotonin and was formerly used in some health food preparations in the belief that it promoted sleep and relieved depression see eosinophilia-myalgia syndrome