HMB, or Beta-Hydroxy Beta-Methylbutyrate, is a metabolite of the branched-chain amino acid leucine.
Branched-chain amino acids, also know as BCAAs, consist of L-leucine, L-isoleucine and L-valine, these are three of the nine essential amino acids. About 35% of muscle protein is comprised of BCAAs, so it is important to have enough available in your body when you are trying to gain and/or maintain muscle.

Ingredients
In a two piece gelatine capsule: Calcium Beta-hydroxy beta-methylbutyrate (HMB), Anti-caking Agents (Magnesium Stearate, Silicon Dioxide).