HMB (beta-hydroxy-beta-methylbutyrate) is made in the body from the amino acid leucine; about 5% of leucine is turned into HMB. As a supplement it is taken to speed recovery from hard training and to help keep or build muscle, including in older adults.
Also known as: beta-hydroxy-beta-methylbutyrate, HMB-Ca, HMB free acid, HMB-FA.
ODS says studies used 1.5 to 6 g a day, most often 3 g, for 1 day to 6 weeks. HMB comes as a calcium salt (HMB-Ca, about 13% calcium, so 3 g adds about 400 mg of calcium) or a calcium-free acid (HMB-FA). These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. ODS says getting 3 g a day of HMB from food is not practical, since it would take more than 600 g of protein a day.
What studies show, per ODS: there is general agreement that HMB helps speed recovery from exercise hard enough to damage muscle, so trained athletes have to push harder to see any effect; some studies suggest gains in strength, power and muscle size. But studies differ so much that it is hard to predict any benefit, there is no expert consensus on taking it for months, HMB is not on the list of evidence-based aids from US sports nutrition groups, and the Australian Institute of Sport does not recommend it outside research. In older adults, a 2021 meta-analysis of 9 trials (448 people) found more fat-free mass with HMB, but no added effect when HMB was combined with exercise. The 2025 ISSN position stand is more positive; several of its authors list affiliations with supplement and nutrition companies (MTI Biotech, AG1, Increnovo).
Safety, per ODS: 3 g a day for 3 to 8 weeks was well tolerated in younger and older adults, with no adverse effects on blood tests, liver or kidney function. It has not been studied in teenagers. The ISSN says safety data extend to at least one year.
We could not find a single published half-life or time to peak for HMB that applies to a supplement dose, so we do not list one. ODS notes that the free acid form appears to raise blood HMB levels faster and higher than the calcium form, but more studies comparing them are needed.
How Dose Track handles peptides · Reconstitution calculator · Half-life calculator