Beta-hydroxy beta-methylbutyrate (HMB)

Leucine metabolite, sport supplement and for sarcopenia. AEMPS does not register as medicine

ATC code: A16AA-HMB

Brand names – supplements: Now HMB, Optimum Nutrition HMB, Bulk HMB, MyHMBSupplements are not tested in clinical trials and are not registered as medications.

Updated 24 Sep 2026 · Methodology

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Muscle mass gain (bodybuilding self-use)

Not recommended

HMB is sold as a «muscle gain» product on the muscle proteolysis inhibition hypothesis. ISSN 2013 position stand recommended HMB 3 g/day for beginning resistance trainees and the elderly; in trained athletes hypertrophy effect is minimal. Sanchez-Martinez 2018 (Clin Nutr) systematic review showed no significant HMB effect on lean body mass in trained athletes. IOC consensus statement 2018 classified HMB as «evidence inconclusive» with potential benefit in resistance training beginners and sarcopenia in the elderly. For muscle gain IOC 2018 lists creatine monohydrate (3–5 g/day), adequate protein (1.6–2.2 g/kg), progressive overload and caloric surplus first-line; HMB is an additional option, not a substitute.

Sources

Sports recovery

Not recommended

HMB is sold as a «post-workout recovery» product on the muscle damage inhibition hypothesis. ISSN 2013 position stand notes moderate reductions in muscle damage markers (CK, LDH) with HMB 3 g/day in resistance training beginners and extreme exercise (marathon, ultra-endurance); in trained athletes the effect is minimal. IOC consensus statement 2018 classified HMB as «evidence inconclusive». For recovery IOC 2018 lists adequate protein and calories, hydration, 7–9 hours of sleep; HMB is an additional option.

Sources

How to read tiers A–F

AStrong evidence – first or second line in international guidelines
BRecommended in selected cases
CStudy data contradict each other
DBenefit not proven, no documented harm
FDocumented harm, or risk without benefit

Mechanism of action

HMB (β-hydroxy-β-methylbutyrate) is a metabolite of the essential amino acid leucine: about 5% of dietary leucine is converted to HMB via α-ketoisocaproate by alpha-ketoacid dioxygenase in the liver. In skeletal muscle HMB inhibits proteolysis via the ubiquitin-proteasome system and reduces autophagy, while stimulating protein synthesis via mTOR signalling. Endogenous HMB production on a regular diet is 0.2–0.4 g/day; exogenous doses 3 g/day × 2–12 weeks raise plasma HMB 3–5 fold. Bioavailability 70%, peak in 1–2 hours, renal excretion.

Safety

Contraindications

Pregnancy and lactation
Children under 18 (outside paediatric trials)
Severe renal impairment
Known hypersensitivity

Serious adverse effects

Allergic reactions (rare)

Common adverse effects

Nausea
Abdominal pain
Mild BP rise (in some studies)

Pregnancy: can you take Beta-hydroxy beta-methylbutyrate (HMB)?

No RCT data in pregnancy. AEMPS does not register as medicine. Avoid in pregnancy.

Breastfeeding: can you take Beta-hydroxy beta-methylbutyrate (HMB)?

No data on milk transfer. Lactating women should avoid.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

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Frequently asked

What is Beta-hydroxy beta-methylbutyrate (HMB) used for?

Beta-hydroxy beta-methylbutyrate (HMB) is evaluated for the following indications with varying evidence strength: Muscle mass gain (bodybuilding self-use) (evidence tier D), Sports recovery (evidence tier D). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Beta-hydroxy beta-methylbutyrate (HMB)?

Common side effects of Beta-hydroxy beta-methylbutyrate (HMB) (≥ 1 in 100): Nausea, Abdominal pain, Mild BP rise (in some studies). See the Safety section for uncommon and serious reactions.

Is Beta-hydroxy beta-methylbutyrate (HMB) safe during pregnancy?

No RCT data in pregnancy. AEMPS does not register as medicine. Avoid in pregnancy.

Is Beta-hydroxy beta-methylbutyrate (HMB) compatible with breastfeeding?

No data on milk transfer. Lactating women should avoid.

Who should not take Beta-hydroxy beta-methylbutyrate (HMB)?

Beta-hydroxy beta-methylbutyrate (HMB) is contraindicated in: Pregnancy and lactation; Children under 18 (outside paediatric trials); Severe renal impairment; Known hypersensitivity. Full list in the Safety section.

Other drugs in this group

L-arginine, Levocarnitine (L-carnitine), L-citrulline (free form and L-citrulline malate for sports formulas), L-glutamine (free amino acid), L-lysine, Lion's Mane Mushroom (Hericium erinaceus), Ademetionine, Chlorophyll (chlorophyllin copper-sodium complex)