What are the side effects of creatine?

Creatine has been shown to be effective in helping to improve strength development, thus assisting with muscle growth, as well as improving anaerobic capacity and explosiveness. But many people don't know how to use creatine correctly to maximize its effects, and whether creatine has potential side effects.

Are you responding to creatine?
Creatine responders and non-responders were mentioned in a 2007 International Society of Sports Nutrition (ISSN) position statement on creatine. That is to say, everyone's response to creatine is different, some people respond very well, and some people don't respond at all. Studies have shown that responders appear to have a higher proportion of type 2 muscle fibers and lower initial creatine reserves, whereas non-responders have a lower proportion of type 2 muscle fibers and higher initial creatine reserves. This means that the effect of creatine is capped, as further increasing creatine reserves will not help non-responders either. The lower your creatine stores before taking creatine, the more likely you are to see improvements in athletic performance, an example of "more is not better". As for how you can tell if you're a non-responder, that's hard to do in a non-clinical setting. But if you're a responder, studies show that after taking creatine for about a month or so, there is a corresponding weight gain due to water retention.

Is Creatine Safe?
Earlier studies using higher doses (20 g per day) found no disease effect. Additionally, studies agree that 5g of creatine per day is safe. Creatine supplementation is considered safe and well-tolerated in humans and animals. In healthy individuals, short-term or long-term use of Creatine monohydrate has not seen any medical side effects. As for kidney health, studies have found that consuming up to 25g of creatine a day is not harmful to kidney function, but only if you don't have previous kidney disease. In addition, Poortmans et al. also found that short-term (5 days), mid-term (14 days), and long-term (10 months to 5 years) intake of creatine did not affect renal function in healthy adults. However, some studies suggest that creatine may increase gastrointestinal discomforts, such as diarrhea, nausea, vomiting, and abdominal discomfort. These side effects can be avoided by consuming small amounts of creatine and drinking plenty of water.

Does creatine interact with caffeine?
So far, only one study in 1996 has found that the two influence each other, and the study has only 9 subjects, and there may be other confounding factors, and the researchers have not been able to explain the mechanism. Three more studies later found that the two do not affect each other, so don't worry about that.