Creatine Supplementation: Benefits and Adverse Effects

Mechanism (background)

Creatine is synthesized endogenously from arginine, glycine, and methionine, and is also obtained from dietary sources (meat, fish) or supplements. In muscle it is phosphorylated to phosphocreatine, which rapidly regenerates ATP during the phosphagen energy system used for short, high-intensity efforts (Harper's Illustrated Biochemistry, 32nd Ed; Miller's Review of Orthopaedics, 9th Ed).

Benefits

Muscle strength, power, and body composition Creatine monohydrate is one of the most extensively studied ergogenic supplements. A 2024 systematic review and meta-analysis found creatine supplementation combined with resistance training produces greater increases in fat-free mass than training alone (PMID: 39074168). It reliably improves strength and power output in short-duration, high-intensity activity by expanding the phosphocreatine pool available for rapid ATP resynthesis.

Exercise performance and recovery

Modest improvements in VO2max have been reported in a 2023 meta-analysis (PMID: 34859731).
Evidence in combat-sport athletes (boxing, martial arts) shows benefits for strength, muscular endurance, and body composition (2025 systematic review, PMID: 40755023).
It supports muscle glycogen replenishment when taken with carbohydrate, and has been studied for reducing exercise-induced muscle damage markers, though results here are mixed (PMID: 33631721).

Clinical/therapeutic uses

In inherited creatine deficiency syndromes (AGAT and GAMT deficiency), creatine supplementation is a genuinely beneficial, disease-modifying therapy - Bradley and Daroff's Neurology in Clinical Practice.
Emerging interest in neuroprotection after traumatic brain injury (largely preclinical/animal data so far, PMID: 37042504), depression as an adjunct (2025 meta-analysis, PMID: 41189312), and cognitive/fatigue support in older adults or people with conditions like long COVID - these areas are promising but less firmly established than the performance benefits. Notably, a 2024 systematic review concluded the theoretical basis for a cognitive-enhancement effect is not well supported by current evidence (PMID: 38582412).

Adverse Effects / Safety Concerns

Most common and well documented

Water retention and mild weight gain, particularly during the initial "loading phase" - this is the most consistently reported side effect (Miller's Review of Orthopaedics, 9th Ed).
Mild GI discomfort (bloating, cramping, occasional diarrhea), usually dose-related and minimized by spreading doses through the day or skipping the loading phase.

Older myths not well supported by current evidence

Dehydration and muscle cramping were traditionally feared (and are still mentioned in some orthopaedic references as a controversy), but larger studies, including in college football players, have found creatine users actually had fewer cramps, heat illness episodes, and muscle strains, not more.
Kidney damage: this concern originated largely from a single 1998 case report. A 2025 systematic review and meta-analysis specifically evaluating kidney function found no significant adverse effect on glomerular filtration or renal function in healthy individuals using standard doses (PMID: 41199218). Creatine supplementation does raise serum creatinine somewhat (a byproduct of increased creatine turnover), which can be misread as reduced renal function on a routine panel even when true GFR is unaffected - this is a monitoring pitfall clinicians should be aware of, not evidence of harm.

Where caution is still warranted

People with pre-existing kidney disease should use creatine only under medical supervision, since most safety data come from studies in healthy individuals.
Long-term safety data extend over two decades of research and are generally reassuring at standard doses (3-5 g/day maintenance, with or without an initial loading phase of ~20 g/day for 5-7 days).
Claims linking creatine to hair loss are based on a single small study showing increased DHT (not hair loss itself) and remain unconfirmed.

A recent pharmacovigilance-style review (2025) analyzing side-effect prevalence across clinical trials and adverse event databases concluded that reported adverse events are generally mild (GI upset, minor weight gain) and that serious adverse events are rare, supporting the position statements from sports nutrition bodies that creatine is safe across the lifespan when used at recommended doses.

Bottom line

For healthy adults, creatine monohydrate at standard doses has one of the strongest safety and efficacy profiles among sports supplements: reliable gains in strength/power/lean mass, reasonably good evidence for improved high-intensity exercise capacity, and no convincing evidence of kidney harm, dehydration, or cramping at recommended doses. The main practical downside is water-retention-related weight gain and occasional GI discomfort. People with kidney disease, or anyone on nephrotoxic medications, should check with a clinician before use.

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