Here is the abstract of a new paper from Medicine and Science in Sports and Exercise, one of the leading international sports journals. Note that although GABA (what's in USN HGH) may increase growth hormone, particularly when combined with resistance training (pumping iron in the gym), there is no data to indicate that it will cause skeletal muscle hypertrophy. So I agree with the previous posts - don't waste your money on supplements, especially here where much research is still needed on the actions and adverse side-effects of oral GABA. Growth hormone isoform responses to GABA ingestion at rest and after exercise. Powers ME, Yarrow JF, McCoy SC, Borst SE. Division of Athletic Training, Shenendoah University, Winchester, VA 22601, USA. mpowers@su.edu Oral administration of the amino acid/inhibitory neurotransmitter gamma aminobutyric acid (GABA) reportedly elevates resting serum growth hormone (GH) concentrations. PURPOSE: To test the hypothesis that GABA ingestion stimulates immunoreactive GH (irGH) and immunofunctional GH (ifGH) release at rest and that GABA augments the resistance exercise-induced irGH/ifGH responses. METHODS: Eleven resistance-trained men (18-30 yr) participated in this randomized, double-blind, placebo-controlled, crossover study. During each experimental bout, participants ingested either 3 g of GABA or sucrose placebo (P), followed either by resting or resistance exercise sessions. Fasting venous blood samples were acquired immediately before and at 15, 30, 45, 60, 75, and 90 min after GABA or P ingestion and were assayed for irGH and ifGH. RESULTS: At rest, GABA ingestion elevated both irGH and ifGH compared with placebo. Specifically, peak concentrations of both hormones were elevated by about 400%, and the area under the curve (AUC) was elevated by about 375% (P < 0.05). Resistance exercise (EX-P) elevated time-point (15-60 min) irGH and ifGH concentrations compared with rest (P < 0.05). The combination of GABA and resistance exercise (EX-GABA) also elevated the peak, AUC, and the 15- to 60-min time-point irGH and ifGH responses compared with resting conditions (P < 0.05). Additionally, 200% greater irGH (P < 0.01) and 175% greater ifGH (P < 0.05) concentrations were observed in the EX-GABA than in the EX-P condition, 30 min after ingestion. GABA ingestion did not alter the irGH to ifGH ratio, and, under all conditions, ifGH represented approximately 50% of irGH. CONCLUSIONS: Our data indicate that ingested GABA elevates resting and postexercise irGH and ifGH concentrations. The extent to which irGH/ifGH secretion contributes to skeletal muscle hypertrophy is unknown, although augmenting the postexercise irGH/ifGH response may improve resistance training-induced muscular adaptations.