Creatine is the number one sports performance supplement available ().
Yet despite its research-backed benefits, some people avoid creatine because they're afraid that it is bad for health.
Some claim it causes weight gain, cramping, digestive, liver or kidney problems ().
However, a review of the evidence suggests these claims are not supported by research ().
This article provides an evidence-based review of creatine's safety and side effects.
The Myths Surrounding Creatine's Side Effects
Depending on who you ask, the suggested side effects of creatine may include:
- Kidney damage.
- Liver damage.
- Kidney stones.
- Weight gain.
- Muscle cramps.
- Digestive problems.
- Compartment syndrome.
Additionally, some people wrongly claim that creatine is an anabolic steroid, that it's unsuitable for women or teenagers or that it should only be used by professional athletes or bodybuilders.
Despite all this, the International Society of Sports Nutrition regards creatine as extremely safe and concludes it is one of the most beneficial sports supplements available ().
Leading researchers who have studied creatine for several decades also conclude that it is one of the safest supplements on the market ().
One study investigated 52 health markers, taking blood samples before and after 21 months of creatine supplementation. They found no adverse effects ().
Creatine has also been used to treat various diseases and health problems, including neuromuscular disorders, concussions, diabetes and muscle loss (, , , ).
Bottom Line: Although there are many claims of side effects and safety issues for creatine, none of them are supported by research.
What Happens to Creatine in the Body?
Creatine is found throughout the body, with 95% being stored in the muscles ().
However, what you get from the diet and is produced in your body is usually not enough to maximize muscle creatine stores.
The average stores are about 120 mmol/kg, but creatine supplements can elevate these stores to around 140–150 mmol/kg, as shown in the graph below ().
During high-intensity exercise, the stored creatine helps the muscles produce more energy. This is the main reason that creatine enhances exercise performance ().
Once you fill your muscle creatine stores, any excess is broken down into creatinine, which is metabolized by the liver and excreted in the urine ().
Bottom Line: 95% of the creatine in your body is stored in muscles. There it provides increased energy for high-intensity exercise.
Does Creatine Cause Dehydration and Cramps?
Creatine alters the body's stored water content, driving additional water into the muscle cells ().
This fact may be behind the theory that creatine causes dehydration. However, this shift in cellular water content is minor, and no research supports the claims about dehydration.
A 3-year study of college athletes found that the creatine group actually had fewer cases of dehydration, muscle cramps or muscle injuries. They also had fewer missed sessions due to illness or injury ().
One study examined creatine use during exercise in the heat, which should normally accelerate cramping and dehydration. During a 35-minute cycling session in 99° F (37° C) heat, researchers found no effects caused by creatine ().
Further examination via blood tests also confirmed no difference in hydration or electrolyte levels, which play a key role in muscle cramps ().
Probably the most conclusive research has been conducted in individuals undergoing hemodialysis, a medical treatment that may cause muscle cramps. Researchers found creatine actually reduced cramping incidents by 60% ().
Based on the current evidence, creatine does not cause dehydration or cramping. If anything, it may actually be protective.
Bottom Line: Creatine use does not increase the risk of cramps and dehydration, and may actually reduce the risk of these conditions.
Creatine and Weight Gain
Research has thoroughly documented that creatine supplements cause a quick rise in body weight.
After 1 week of high-dose loading of creatine (20 grams/day), weight increases by around 2–6 lbs (1–3 kg) due to increased water in the muscles (, ).
Over the long term, studies have shown that body weight may continue to increase to a greater extent than in non-creatine users. However, weight gain is due to increased muscle growth and not increased body fat ().
For most athletes, the additional muscle is a positive adaptation that may improve sports performance. It is also one of the main reasons people take creatine, so it should not be considered as a "side effect" (, ).
Increased muscle may also have benefits for people such as the elderly, individuals with obesity and those with certain diseases (, , , , ).
Bottom Line: Weight gain from creatine is due to increased water content within the muscle and long-term muscle growth, not fat storage.
Creatine's Effects on the Kidneys and Liver
Creatine can slightly raise levels of creatinine in the blood. Creatinine is commonly measured to diagnose kidney or liver problems.
However, the fact that creatine raises creatinine levels does not mean that it is harming your liver or kidneys ().
To date, no study of creatine use in healthy individuals has provided evidence of harm to these organs (, , , , , ).
A long-term study of college athletes found no side effects related to liver or kidney function. Other studies measuring biological markers in the urine also found no difference after creatine supplementation ().
One of the longest studies to date, lasting 4 years, similarly concluded that no negative side effects resulted from creatine supplements ().
Another popular study often cited in the media reported kidney disease in a male weightlifter who supplemented with creatine ().
However, considering the thousands of users and many studies showing no problems, this single case study is insufficient evidence. There were also numerous other factors involved, including additional supplements (, ).
All this being said, creatine supplements should be approached with caution if you have current or previous liver or kidney issues.
Bottom Line: Current research suggests that creatine does not cause liver or kidney problems in healthy people.
Does Creatine Cause Digestive Problems?
As with many supplements or medications, doses larger than recommended may cause digestive issues.
In one study, the 5-gram recommended dose caused no digestive problems, while a 10-gram dose increased the risk of diarrhea by 37% ().
For this reason, the recommended serving is set at 3–5 grams. The 20-gram loading protocol is also split into 4 servings of 5 grams each over the course of a day ().
Leading creatine researcher R.B. Kreider reviewed the data from several of his past creatine studies and concluded there was no increase in digestive problems ().
However, it is possible that additives, ingredients or contaminants generated during the industrial production of creatine can lead to problems (, ).
It is therefore recommended to purchase a trusted, high-quality product.
Bottom Line: Creatine does not increase digestive issues when the recommended dosages and loading guidelines are followed.
Creatine and Drug Interactions
As with any diet or supplement regimen, it is always a good idea to discuss your plans with a doctor or other medical professional before you start.
You may also wish to avoid creatine supplements if you are taking any medications that affect liver or kidney function.
Such medications may include cyclosporine, aminoglycosides, gentamicin, tobramycin, anti-inflammatory drugs like ibuprofen and numerous others ().
Creatine can help improve blood sugar management, so if you are using medication known to affect blood sugar, you should discuss creatine use with a doctor ().
You should also discuss creatine use with a doctor if you are pregnant, breastfeeding or have a serious condition such as heart disease or cancer.
Bottom Line: Creatine may cause problems if you take certain types of medications, including medications that affect blood sugar levels.
Other Suggested Side Effects of Creatine
Due to increased water content within the muscle, some people suggest creatine can lead to compartment syndrome — a condition that occurs when excessive pressure builds inside an enclosed space, usually within the arm and leg muscles.
Although one study found an increase in muscle pressure during 2 hours of heat training, it resulted mainly from heat and exercise-induced dehydration ().
Researchers also concluded the pressure was short-lived and insignificant.
Rhabdomyolysis, a condition where muscle breaks down and leaks harmful proteins, is also said to increase with creatine. This myth originated because a marker in the blood called creatine kinase increases with creatine supplements ().
However, this slight increase is quite different from the large amounts of creatine kinase associated with rhabdomyolysis. Interestingly, some experts even suggest creatine may be protective against this condition (, ).
Some people also confuse creatine with anabolic steroids, but this is yet another myth. Creatine is a completely natural and legal substance found in the body and in foods such as meat, with no link to steroids ().
Finally, there is a misconception that creatine is suitable only for athletes and unsafe for elderly people, women or children. The truth is that there is no research to suggest it is unsuitable in recommended doses for women or the elderly ().
Unlike most supplements, creatine has actually been used in children as a medical intervention for conditions such as neuromuscular disorders and muscle loss.
Studies lasting as long as 3 years have found no negative effects of creatine in children (, , ).
Bottom Line: No evidence supports any of the myths surrounding creatine, and research has consistently confirmed its excellent safety profile.
Creatine Has an Outstanding Safety Profile
Creatine has been around for more than a century and over 500 studies support its safety and effectiveness.
It also provides many benefits for muscle and performance, may improve markers of health and is being used in medical settings to treat a variety of diseases (, , ).
At the end of the day, creatine is one of the cheapest, most effective and safest supplements available. Period.
This article has much more detailed information on creatine: Creatine 101 – What is it and What Does it do?