Is it safe to take melatonin (a hormone that regulates sleep-wake cycles) before exercise?

Melatonin Before Exercise: Safety and Considerations

Taking melatonin before exercise is generally safe from a physiological standpoint, but it is not recommended due to its hypnotic and hypothermic effects that can impair both mental and physical performance during and immediately after administration. 1

Immediate Performance Effects

• Exogenous melatonin administration leads to hypnotic (sleepiness-inducing) and hypothermic (body temperature-lowering) responses in humans, which are directly linked to immediate reductions in short-term mental and physical performance 1
• These performance-impairing effects appear to be short-lived for physical activities, though cognitive performance may remain affected for 3-5 hours after administration depending on the dose 1
• The timing of melatonin administration is critical—it should be taken 1.5-2 hours before desired bedtime, not before exercise 2

Impact on Endogenous Melatonin Production

• Exercise timing significantly affects natural melatonin secretion patterns: afternoon exercise (16:00 h) blunts melatonin secretion compared to morning exercise (09:00 h), with salivary melatonin levels at 22:00 h measuring 13.7 pg/mL after afternoon exercise versus 16.5 pg/mL after morning exercise 3
• Postural changes and exercise can actually increase endogenous melatonin levels, which is an important confounding factor when measuring circadian rhythms 4
• If sleep quality is a concern for athletes, morning exercise may be preferable to afternoon exercise to preserve natural melatonin secretion patterns 3

Safety Profile for Athletic Populations

• A study examining 5 mg of melatonin ingested before sleep by physically-active subjects found no meaningful effects on physical performance the following morning, with mean differences less than 1% for strength tests and cycling time trials 5
• The confidence intervals for performance differences were narrow: -2.1 to 2.8 kg for left grip strength, -3.1 to 2.7 kg for right grip strength, and -3.0 to 4.5 seconds for a 4 km cycling time trial 5
• There was little evidence that melatonin improved sleep quality in this fit population, suggesting limited benefit for athletes with normal sleep patterns 5

Physiological Mechanisms Relevant to Exercise

• Melatonin works by binding to M1 and M2 receptors, suppressing REM sleep motor tone and renormalizing circadian features of sleep 2
• The hormone's hypothermic effects theoretically could improve endurance performance in hot environments by lowering core body temperature, but this hypothesis has not been supported by evidence from studies with military recruits exercising at low intensities 1
• No research has examined this hypothesis with athletes exercising at high intensities, leaving this potential benefit unproven 1

Practical Recommendations

• Do not take melatonin before exercise—reserve it for evening use 1.5-2 hours before bedtime when circadian phase shifting or sleep promotion is the goal 2
• If using melatonin for sleep optimization in athletes, start with 3 mg of immediate-release formulation 2
• Higher doses (10 mg) may cause receptor desensitization and are associated with more frequent adverse effects including morning headache and sleepiness 2
• Choose United States Pharmacopeial Convention Verified formulations for reliable dosing, as melatonin is regulated as a dietary supplement with concerns about purity and stated dose accuracy 2, 6

Important Caveats

• Melatonin concentrations are suppressed by light even at levels lower than typical room lighting, so assessment of endogenous levels requires dim light conditions (<5 lux) 4
• A washout period of 72 hours for NSAIDs and 24 hours for caffeine and alcohol should occur before melatonin assessment, as these substances affect melatonin levels 4
• Use with caution in patients taking warfarin or those with epilepsy due to potential interactions 6
• Melatonin has been associated with impaired glucose tolerance in healthy individuals after acute administration, warranting caution in athletes with metabolic concerns 6