Creatine supplementation leads to rapid weight gain (1-3 kg) in the first few days due to water retention in muscle, which is distinct from muscle hypertrophy caused by strength training.

Cr supplementation leads to weight gain within the first few days, likely due to water retention related to Cr uptake in the muscle... Retention of Cr in the skeletal muscle would result in muscle enlargement due to water absorption; however, this short-term skeletal muscle enlargement is not typical of that induced by 'strength' training, which results in the accrual of contractile and structural protein that is associated with 'true' muscle hypertrophy.