L-Leucine

Best for

Build more muscle from protein

Promising early signal · 11–3000 mg/kg/day/day for 1–52 weeks · 3 studies , n=96

12 papers · 5 claims · 56 outcomes scored · 4 positive

Outcomes

What l-leucine actually does, by outcome

Each row is one outcome with effect size, evidence base, the dose that worked in trials, and time to first effect. Magnitude tiers come from native-unit MCID where available, Cohen's d otherwise.

Outcome Effect size Evidence Dose Weeks Rank

Boost sprint speed and peak power Likely benefit

More watts and faster times in short all-out efforts.

1 meta-analysis n=394 — — #5/21

41373993

moderate

1 meta-analysis n=394 Meta-analyzed

—

#5 /21

Build more muscle from protein Promising early signal

Every gram you eat goes further toward repair instead of being burned as fuel.

3 RCTs n=96 11–3000 mg/kg/day 1–52 wk #1/3

11593302·26081485·27101760

moderate

3 RCTs n=96

11–3000 mg/kg/day

1–52 wk

#1 /3

Build stronger muscles Faint early signal

Higher one-rep max, stronger grip, and more force from every muscle group.

4 meta-analyses n=607 6–21 g 12–24 wk

26081485·33871558·32230954·40717998

small

4 meta-analyses n=607 Meta-analyzed

6–21 g

12–24 wk

—

Lose body fat Proven but unnoticeable

Body fat percentage drops and the mirror shows it before the scale does.

2 meta-analyses n=439 3–7.2 g 8 wk #4/56

37923932·40717998

trivial

2 meta-analyses n=439 Meta-analyzed

3–7.2 g

8 wk

#4 /56

Jump higher and react faster Probably doesn't help

More explosive takeoff force and quicker ground contact.

1 meta-analysis n=593 — —

41373993

trivial

1 meta-analysis n=593 Meta-analyzed

—

Outcome	Effect	Evidence	Dose	Weeks	Rank
Boost sprint speed and peak power Likely benefit	moderate	1 meta-analysis n=394 Meta-analyzed	—	—	#5/21
Build more muscle from protein Promising early signal	moderate	3 RCTs n=96	11–3000 mg/kg/day	1–52 wk	#1/3
Build stronger muscles Faint early signal	small	4 meta-analyses n=607 Meta-analyzed	6–21 g	12–24 wk	—
Lose body fat Proven but unnoticeable	trivial	2 meta-analyses n=439 Meta-analyzed	3–7.2 g	8 wk	#4/56
Jump higher and react faster Probably doesn't help	trivial	1 meta-analysis n=593 Meta-analyzed	—	—	—

Buy well

Recommended L-Leucine products

Real products that dose L-Leucine where the research does, in a clean formulation, from brands we've audited. We only list ones we'd stand behind.

Chosen for adequate L-Leucine dosing vs. the studied range, a clean formulation (grade A–C), and independent brand-quality audits. Not sponsored.

Risk profile

Adverse events and known drug interactions

Safety events

gastrointestinal symptoms (nausea, bloating, diarrhea, constipation, reflux)

valine_and_isoleucine_depletion

blood_ammonia_increase

reduced_isoleucine_and_valine_plasma_concentrations

Sources

Generated August 14, 2026

L-Leucine

What l-leucine actually does, by outcome

Recommended L-Leucine products

Adverse events and known drug interactions

More evidence for L-Leucine

The White Crystal That Flips a Muscle Switch—and the Paradox It Reveals

BCAA

Carnitine

Collagen

Creatine

Whey Protein

L-Leucine

Recommended L-Leucine products

More evidence for L-Leucine

NewThe White Crystal That Flips a Muscle Switch—and the Paradox It Reveals

NewBCAA

NewCarnitine

NewCollagen

NewCreatine

NewWhey Protein

The White Crystal That Flips a Muscle Switch—and the Paradox It Reveals

BCAA

Carnitine

Collagen

Creatine

Whey Protein