GABA is a popular supplement many use to improve sleep and studies show that it may also boost growth hormone production! One side effect many have reported is weird dreams/nightmares so keep that in mind when you go to bed. It’s inconclusive if this will have any major effect on gains but it’s worth trying to see if GABA can improve your sleep quality.
Reference: Cavagnini, F., Invitti, C., Pinto, M., Maraschini, C., Di Landro, A., Dubini, A., & Marelli, A. (1980). Effect of acute and repeated administration of gamma aminobutyric acid (GABA) on growth hormone and prolactin secretion in man. Acta Endocrinologica, 93(2), 149-154.