Creatine Monohydrate

Claimed to increase muscle strength, power, lean or fat-free mass and high-intensity exercise capacity, and marketed increasingly for cognition, bone health and healthy ageing. The strength and body-composition claims are among the best-evidenced in this cluster: hundreds of randomised trials, pooled in the largest synthesis to date across 143 studies, and two authorised health claims in the European Union — one for physical performance in successive bursts of short-term high-intensity exercise, one for the effect of resistance training on muscle strength in adults over 55.

The effects are real and small. The pooled figures are +0.86 kg body mass, +0.82 kg fat-free mass and −0.28% body fat, with no heterogeneity at all across studies — the authors’ own word for this is a "small effect". Part of the fat-free-mass gain is water rather than contractile tissue: NIH ODS notes creatine often causes weight gain from water retention, and when the outcome is measured as direct regional muscle thickness instead of whole-body mass the pooled estimate crosses zero.

Safety knowledge is established, with hundreds of trials from 7 to 52 weeks plus multi-year follow-up noted by NIH ODS, and no hepatotoxicity signal. No tolerable upper intake level has been set. The frequently-asserted absence of renal harm could not be verified from a dedicated safety meta-analysis and is recorded here as unverified rather than confirmed.