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Amino Acid

L-Leucine

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L-Leucine. Essential BCAA and primary anabolic signaler via mTORC1 activation.

How it works. Activates mTORC1 directly via Sestrin2-GATOR2.

What the research supports. 2 graded claims. Strongest: Triggers MPS at ~3 g/meal (strong).

How much to take. Typical dose: 2.5–5 g per dose; 3 g optimal MPS trigger.

Side effects and interactions. 1 medication interaction listed. Serious: Discontinue and seek medical advice if symptoms are severe, persistent, or include difficulty breathing.

Stacking. Pairs well with Creatine monohydrate, Whey or EAAs.

Common forms. Available as L-Leucine, HMB (metabolite).

Key studies. 9 studies cited. The strongest are listed with links to PubMed.

Community. Experiences from people who have tried L-Leucine. Anecdotes are not medical advice.

L-Leucine. Essential BCAA and primary anabolic signaler via mTORC1 activation.

Molecular structureC6H13NO2 · 131.17 g/mol

What it is

Essential BCAA and primary anabolic signaler via mTORC1 activation.

Food sources

WheyEggsMeat

Goals

Muscle GrowthAthletic Performance

How it works

Activates mTORC1 directly via Sestrin2-GATOR2.

Pathways

  • mTORC1

Effects

  • +Muscle protein synthesis supports

What the research supports

Triggers MPS at ~3 g/mealstrong
Improves recovery in elderly with low protein intakemoderate

Strong: consistent results across large trials or meta-analyses. Moderate: several trials, mostly positive. Limited: small or mixed studies. Preclinical: animal or cell research only.

Typical dose
2.5–5 g per dose; 3 g optimal MPS trigger
TimingConsistent daily timing recommended; split larger doses if GI tolerance is a concern.
With foodEither with or without food.
Best formMost evidence is based on the l-leucine form.
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Side effects & interactions

Common side effects

  • L-Leucine is generally well-tolerated at evidence-based doses
  • Mild GI discomfort (nausea, loose stools, or bloating) possible at higher intakes
  • Headache or transient fatigue reported by a small fraction of users

Serious

  • Discontinue and seek medical advice if symptoms are severe, persistent, or include difficulty breathing

Medication interactions

Prescription medications (general)minor

Always disclose L-Leucine use to your prescriber — additive, antagonistic, or pharmacokinetic interactions are possible.

Check any supplement–medication combination with your pharmacist before starting.

Combines with

Pairs well

  • Creatine monohydrateFoundational support for strength, power, and lean mass.
  • Whey or EAAsProvides amino acid substrate for muscle protein synthesis.

Common forms

  • L-Leucine
  • HMB (metabolite)

Key studies

9 studies cited in total.

PubMed: L-Leucine — Triggers MPS at ~3 g/meal ↗
Systematic review · PubMed (NLM) · 2026

Opens current human and preclinical literature matching L-Leucine and "Triggers MPS at ~3 g/meal". Filter by RCT, meta-analysis, or year on the results page.

PubMed: L-Leucine — Improves recovery in elderly with low protein intake ↗
Systematic review · PubMed (NLM) · 2026

Opens current human and preclinical literature matching L-Leucine and "Improves recovery in elderly with low protein intake". Filter by RCT, meta-analysis, or year on the results page.

PubMed: L-Leucine — randomized controlled trial ↗
Systematic review · PubMed (NLM) · 2026

Opens current human and preclinical literature matching L-Leucine and "randomized controlled trial". Filter by RCT, meta-analysis, or year on the results page.

Discussion

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