How many grams of creatine per day is worthwhile?
For muscle strength and explosive performance, 3 to 5 grams of creatine monohydrate per day has a clear effect; a loading phase is convenient but not obligatory. For other goals the evidence is thinner, but safety for healthy adults is reasonably well supported.
How you take creatine depends on what you want to achieve. For muscle strength and lean mass, 3 to 5 grams per day is the best-supported choice, maintained for at least 8 to 12 weeks. You do not need a loading phase for this: daily low doses without a pre-loading period also work. Always use creatine monohydrate; for other forms (HCl, ethyl ester, citrate) there is no evidence that they work better, and creatine ethyl ester has a specific drawback: it raises a blood marker that mimics kidney function, which can lead to a false diagnosis.
If you want to reach full muscle saturation more quickly, a traditional loading phase of 20 grams per day is used, divided over four doses, for 5 to 7 days. After that, a maintenance dose of 2 to 5 grams per day is sufficient to sustain the elevated muscle creatine levels. Two grams per day alone proved in research to be just insufficient to keep phosphocreatine levels fully topped up as well; 3 to 5 grams is more reliable. The effect of creatine is clearly present during short, explosive exercise and repeated sprints. No benefit has been demonstrated for endurance sports.
For cognition during sleep deprivation or mental stress, a short loading phase of 20 grams per day for 5 to 7 days has been used in research. Whether this protocol is also useful for cognition outside of athletes has not been properly investigated yet; the evidence is preliminary. If you want to try it for this purpose, discuss it with your doctor, especially if you are taking medication.
Creatine is well tolerated in the short term by healthy adults. Possible side effects include weight gain (partly due to fluid retention), cramps, diarrhoea and dizziness. Kidney problems have been described in only two isolated cases and have not been demonstrated in healthy people in controlled research. Caution is advised for people with existing kidney disease, diabetes or high blood pressure; discuss it with your doctor first in those cases. Pay attention to product quality as well: not all creatine supplements meet pharmaceutical quality standards, so choose a product with an independent quality certification.
The evidence comes from multiple randomised studies and reviews. The studies on dosing and muscle creatine levels are relatively robust, but many reviews on cognition and some safety data are based on small or observational studies. One review on brain effects was co-authored by authors with financial ties to a creatine manufacturer, which may colour the conclusions. The safety data at lower doses are fairly consistent; for higher doses over the long term (above 10 grams per day) the data are thin.