According to Men's Health, creatine and beta-hydroxy-beta-methylbutyrate (HMB) are two supplements with research-proven effects of lean mass gain, although HMB has undergone less testing compared to creatine. Supplements that claim to boost testosterone levels, such as tribulus terrestris, have failed in research studies.
WebMD explains that creatine is a substance that transforms into the chemical creatine phosphate when metabolized. Subsequently, creatine phosphate is used to make the energy-producing compound adenosine triphosphate (ATP) within cells, providing the necessary energy for muscle contraction. It is believed that creatine provides additional energy for quick bursts of high-intensity exercise. According to WebMD, creatine supplementation is believed to increase muscle mass and help muscles recover from intense training.