Does HMB actually build muscle?

Short answer

Not for people who train. In an analysis of 302 people, lean mass and strength were no different from those who did not take HMB, and the same held for 561 people who did strength training.

Does HMB actually build muscle?
'Less muscle breakdown → more muscle' — does this formula hold?
HMB is what your body makes from leucine, a building block of protein. It is sold as a way to block muscle breakdown and grow more muscle. We checked, study by study, whether this holds for people who actually train.
It started with a bang
A study reported 7.4 kg of muscle in 12 weeks
A 2014 study recruited 24 people and analyzed the 20 who finished. After 12 weeks, the HMB group gained 7.4 kg of lean mass (muscle and everything except fat). The placebo group gained 2.1 kg. This result made HMB famous.
When others repeated it, it didn't hold
44 people, 12 weeks: all three groups gained about the same
44 people who already ate plenty of protein took one of two HMB forms or a placebo for 12 weeks. Lean mass rose 1.8 kg, 0.8 kg and 0.9 kg, with no difference between groups, and soreness was not reduced. Only one measure, leg press strength, rose slightly more.
Pooling the studies: no difference
Analysis of 302 people: no gain in muscle or strength
A 2020 analysis of 302 people found a lean mass difference of 0.29 kg, which was not a meaningful difference, and strength was the same. Results like 7.4 kg stood far apart from other studies and were left out; the researchers noted that size matches what testosterone injections produce.
Another analysis: same answer
Analysis of 193 people: no change in strength or body weight
An analysis of 193 people found no difference in bench press or leg press strength or in lean mass. Splitting by dose and duration changed nothing. Another analysis of 161 people found a small effect only when protein intake was low (under 112 g a day for a 70 kg (154 lb) person).
What about taking it without exercise?
HMB alone helps a little; with exercise, no difference
A 2025 analysis of 1,935 people found HMB added 0.28 kg of lean mass and 0.54 kg of grip strength. But a 2026 analysis of 561 people who also did strength training found no added effect of HMB on muscle mass or strength.
Bottom line: HMB adds nothing for people who train
Protein and training come first
For people who lift, HMB did not add muscle or strength, and the big early results were never confirmed. Eating enough protein (112 g or more a day for a 70 kg person) and training consistently is enough; adding HMB on top did not change the outcome.