Creatine
Most extensively studied performance supplement. Increases phosphocreatine stores for ATP regeneration in high-intensity exercise. Used for strength, power, lean mass, and increasingly for neuroprotection. Excellent long-term safety record.
How it works (mechanism of action)
Phosphorylated by creatine kinase to phosphocreatine (PCr) serving as immediate phosphate buffer to regenerate ATP from ADP during maximal-intensity exercise. Osmotically active increasing intracellular water content stimulating satellite cell activation for muscle hypertrophy.
Evidence grades: A=Strong RCT evidence · B=Good clinical trials · C=Limited trials · D=Preliminary/traditional
Renal disease: CONTRAINDICATED in pre-existing kidney disease (creatine increases creatinine — confounds renal markers). Water retention: 1-3kg initial water weight gain. Interstitial nephritis (rare — case reports). Drug interactions: nephrotoxic drugs (NSAIDs, aminoglycosides — additive renal stress). Generally extremely safe in healthy individuals. Inform renal function testing.