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Glycerol

Glycerol (glycerin) is a sweet, syrupy compound that some endurance athletes drink with a large volume of fluid before exercise in the heat, so that the body holds extra water. Trials and a meta-analysis found it keeps more fluid in the body than water alone, but its effect on endurance performance is mixed, with several recent trials finding no gain. Nausea, bloating and stomach upset are the usual side effects. The World Anti-Doping Agency prohibited it in 2010 and removed it from its list in 2018, and glycerol slush drinks have made young children seriously ill.

Sources: PMID 17962713; PMID 36771308; PMID 37490269; PMID 40068898

Best evidence
Grade B: moderate evidence

What glycerol is good for

How we grade →

  • Dehydration

    Moderate evidence

    Hydration (Total Body Water): Improves · 4 studies

    Studied as: Healthy, active adults drank glycerol (about 1 g per kg of body weight) mixed into a large drink of water or diluted sports drink in the hours before exercise, compared with the same drink without glycerol; measured as extra fluid kept in the body over the following hours. This is about preventing dehydration in healthy people, not treating it.

    Reviewed

    All 1 outcome ↓

Is glycerol safe?

Safety note. Talk to a doctor or pharmacist before you start glycerol if you take prescription medicines, are pregnant or breastfeeding, or have a long-term health condition. Supplements can interact with medicines.

Evidence by condition

  • Strong
  • Moderate
  • Limited
  • Very limited
B

Dehydration

▲ Hydration (Total Body Water)1 outcome · 4 studies

Dehydration: all the evidence on its own page

Dehydration: outcomes studied for Glycerol
GradeOutcomeEffectSize and studies
BHydration (Total Body Water)ImprovementStudied as: Healthy, active adults drank glycerol (about 1 g per kg of body weight) mixed into a large drink of water or diluted sports drink in the hours before exercise, compared with the same drink without glycerol; measured as extra fluid kept in the body over the following hours. This is about preventing dehydration in healthy people, not treating it.
Studies that measured hydration (total body water) (4 studies)
Improves4 studiesReviewed
C

Aerobic Exercise Performance

Endurance Exercise Performance1 outcome · 6 studies

Aerobic Exercise Performance: all the evidence on its own page

Aerobic Exercise Performance: outcomes studied for Glycerol
GradeOutcomeEffectSize and studies
CEndurance Exercise PerformanceMixed effectStudied as: Trained or recreationally active adults drank glycerol (about 1 to 1.2 g per kg of body weight) in a large drink in the 2 hours before endurance exercise, compared with the same volume of drink without glycerol; results disagree between trials.
Studies that measured endurance exercise performance (6 studies)
6 studiesReviewed
C

Warm- or Hot-Weather Exercise Performance

Endurance Exercise Performance1 outcome · 3 studies

Warm- or Hot-Weather Exercise Performance: all the evidence on its own page

Warm- or Hot-Weather Exercise Performance: outcomes studied for Glycerol
GradeOutcomeEffectSize and studies
CEndurance Exercise PerformanceMixed effectStudied as: Trained adults drank glycerol (about 1 to 1.2 g per kg of body weight) in a large drink in the 2 hours before endurance exercise in the heat (32 to 35 C or warm and humid), compared with the same volume of drink without glycerol; trials disagree.
Studies that measured endurance exercise performance (3 studies)
3 studiesReviewed