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Limited evidencePhysical performance

HMB (β-Hydroxy-β-Methylbutyrate)

HMB is a leucine metabolite with an unusually polarised literature: early industry-linked trials reported large gains that independent meta-analyses in trained young people have failed to reproduce. The more defensible use is anti-catabolic — older adults, bed rest and clinical muscle wasting — not building muscle in healthy lifters.

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What the science says

  • Increasing muscle mass and strength in trained young adults Limited evidence

    Jakubowski's 2020 systematic review and meta-analysis concluded HMB does not improve resistance-exercise-induced changes in body composition or strength in young subjects. The famously large effects reported in a handful of trials (gains of several kilos of lean mass in weeks) have never been independently replicated and are widely regarded as implausible.

  • Preserving muscle in older adults and during disuse Moderate evidence

    A 2019 systematic review with meta-analysis in older adults found HMB added to exercise produced small improvements in muscle mass and some strength measures. The 2025 ISSN position stand similarly concludes HMB is most useful as an anti-catabolic agent in older, untrained or clinically compromised populations rather than as an anabolic in athletes.

  • Reducing exercise-induced muscle damage Moderate evidence

    HMB modestly attenuates markers of muscle damage such as creatine kinase and LDH after unaccustomed or intense exercise, an effect the ISSN position stand supports. The effect is most visible in untrained participants performing novel damaging exercise, where there is more damage to attenuate.

Dosage & safety

Studied dose3 g/day is the near-universal study dose, usually split into three 1 g doses with meals, or 1 g taken 60-120 minutes pre-exercise. Free-acid HMB is absorbed faster than the calcium salt (HMB-Ca), but has not been shown to produce better outcomes. Studies typically run 4-12 weeks; the anti-catabolic effect requires consistent daily use, not just pre-workout dosing.
SafetyOne of the better-tolerated sports supplements; trials up to 6 g/day for 12 weeks report no meaningful adverse effects on liver enzymes, kidney function or lipids. Long-term (>1 year) safety data are sparse. Not prohibited by WADA. Because HMB is heavily marketed on discredited data, be sceptical of products bundling it at trivial doses.

How to take it

TimingSplit into three 1 g doses with meals, or take 1 g 60-120 minutes before training.
With food?With food for the split-dose schedule; the free-acid form absorbs faster but this has not translated into better results.
Worth knowingDaily consistency is what the anti-catabolic case rests on, so a pre-workout-only habit misses the mechanism entirely.

Frequently asked questions

Does HMB build muscle?

Not in trained young adults — the evidence is limited. A 2020 meta-analysis found HMB does not improve muscle or strength gains from resistance training in young people, and early large effects were never independently replicated.

Who can benefit from HMB?

HMB has moderate evidence as an anti-catabolic in older adults: added to exercise, HMB produced small gains in muscle mass and some strength measures, which the 2025 ISSN position stand also supports.

How much HMB per day?

The standard HMB dose is 3 g/day, usually split into three 1 g doses with meals. Take HMB every day, because the anti-catabolic effect depends on consistency, not pre-workout timing.

Is HMB safe?

HMB is one of the better-tolerated sports supplements: trials up to 6 g/day for 12 weeks found no meaningful effects on liver, kidney or lipids. Long-term safety data beyond a year are sparse.

Scientific references

Where to buy

Double Wood Supplements, HMB, 120 Capsules

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