Pooled randomised trials in 303 young, fit people given growth hormone found 2.1 kg more lean body mass (95% CI 1.3-2.9) but no apparent gain in strength or exercise capacity, higher exercise lactate in 2 of 3 studies that measured it, and more soft-tissue swelling and fatigue, so the authors judged claims that growth hormone improves performance unsupported; from the abstract

Liu and colleagues pooled randomised trials that gave growth hormone or no growth hormone to healthy, physically fit people aged 13-45, to test the belief that it improves athletic performance. Forty-four articles describing 27 study samples qualified, with 303 people on growth hormone for 13.3 person-years in all.

Lean body mass rose by 2.1 kg more than without the hormone, but strength and exercise capacity did not appear to improve; exercise lactate was higher in 2 of 3 studies that measured it, and swelling and fatigue were more common.

The authors conclude that performance claims are not supported by the literature, that growth hormone may not improve strength and may worsen exercise capacity and raise adverse events, and that more research is needed.

303 participants received growth hormone; mean age 27 (SD 3) y, BMI 24 (SD 2) kg/m², VO2max 51 (SD 8) mL/kg/min; healthy, lean, physically fit, community-dwelling.