Glycine
Uses it2 g every third or fourth night, together with 100 mg GABA
Huberman says he adds glycine to his sleep routine on some nights rather than nightly.
“every third or fourth night, I will take two grams of glycine and 100 milligrams of GABA”Andrew Huberman
Source: Sleep Toolkit: Tools for Optimizing Sleep & Sleep-Wake Timing (podcast, 8 Aug 2022)