Creatine is, without a doubt, one of the most popular sports supplements of our time. Given how directly people associate it with improved performance and body composition you could even place it ahead of whey protein powder, which many athletes now seem to treat like a food—or, in some cases, a food group.

Part of creatine's appeal is, of course, due to its effectiveness. Most of the people who take it simply see greater strength, power, and muscle growth as a result, and the research backs this up. Creatine also happens to be one of the most studied supplements, both in a sports setting and in how it interacts with various medical conditions. In short, if you're not taking creatine because you're afraid of a certain side effect, that side effect has probably been looked at in a laboratory setting.

Want the straight truth about what creatine will or won't do to your heart, liver, or kidneys? Here's what the existing research has to say.

General Side Effects and Concerns

First off: Yes, creatine can cause water retention. This is probably no surprise. Regardless, unless you have a specific concern—like hypertension that requires treatment with diuretics—it's not a medical issue. For people concerned about looking bloated, the water retention happens in your muscles, so it actually makes you look a bit larger. This explains why some bodybuilders cut out creatine near the end of their contest prep. The rest of us needn't worry.

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Regarding other potential side effects:

• Stomach distress. This can happen when you take too much creatine at once, perhaps during a loading phase, without much else in your stomach. The remedy is usually simple: either increase your water and food intake when you take creatine or just take smaller doses of creatine throughout the day.
• Intestinal distress or diarrhea. This also can happen when you simply take too much creatine in a single dose. Since it cannot be absorbed in high quantities, this can cause osmotic diarrhea, a condition where water gets drawn into the bowels. The solution, again, is to take smaller doses.

All of the common side effects associated with creatine stem from its absorption profile in the intestines. At low doses, around 1-3 grams, creatine is absorbed well. As the dose gets higher, the absorption decreases, which is why you can't overdose on creatine—at least, not in a way that would present a medical concern.

There are some claims that creatine can contribute to cardiovascular issues such as arrhythmia, but they seem to be based on anecdotes and the placebo effect.

What About The Liver?

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A common knock against creatine is that it's bad for the liver, but this doesn't withstand scrutiny. A number of human studies have looked specifically at creatine usage and liver parameters and found no association between the supplement and liver problems.1,2

If you really want to go cherry-picking, a single study found liver problems in a particular mouse strain after 300 days of supplementation.3 Even with that in mind, human studies done on people with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's Disease, over a span of 9-16 months failed to find any problems with liver enzymes.4-6

What About The Kidneys?

The idea that creatine could cause kidney damage comes from the following logic:

1. One of the tests for a malfunctioning kidney is for creatinine. If the creatinine levels in your blood are high, your kidneys could be malfunctioning.
2. Creatinine is a waste product of creatine, and loading creatine will increase your creatinine levels.

Elevated creatinine levels in and of themselves aren't a problem. They can be indicative of kidney problems, but they can also occur independent of kidney problems. On some level, it's understandable that this caused someone to sound the alarm, but it doesn't make it a reason to avoid taking creatine.

Human studies on biomarkers of kidney function during creatine supplementation have shown no significant alterations in BUN (blood urea nitrogen) or urinary glucose or proteins, and GFR (glomerular filtration rate) also remained unaffected. This was shown in people with ALS,4-6 postmenopausal women,7 athletes,8 young adults,9-11 and type-2 diabetics.12 Even a dose of 2 grams was shown to be fine for dialysis patients over the course of four weeks.13

Rat studies on a model with two-thirds nephrectomy—literally removing 66 percent of the kidney—found no issues with creatine.14,15 There is also a case study of a man with a single kidney having no problems with 20 grams of creatine daily alongside his high-protein diet.16

One rat study did show harm in rats with polycystic kidney disease.17 What's more, a single human case study that noted an accelerated rate of kidney damage in a man with focal segmental glomerulosclerosis (FSG). The impairment stopped when the supplement was removed, and started again when reintroduced.18 Both of these conditions are characterized by kidney tissue edema, a swelling caused by water accumulating. It has been suggested that any kidney issues that cause edema could be made worse with creatine—or anything that causes water retention in this organ.

The Bottom Line

Looking at the current body of research, it's safe to say:

1. Creatine does not cause damage to skeletal muscle or the heart, liver, or kidneys.
2. Creatine, at this moment in time, seems to be fine for kidney disorders that are not characterized by edema and tissue swelling.
3. Based on limited research, it is probably wise to avoid creatine supplementation if you have polycystic kidney disease, focal segmental glomerulosclerosis, or another kidney disorder characterized by tissue swelling.

Creatine is one of the most commonly viewed topics on our website, Examine.com. We've pored over the research, and we see no reason to fear creatine (more creatine myths debunked). Modern athletes treat it like a vitamin, and with good reason: It's safe, healthy, cheap, and for most people, it simply works. Get some creatine monohydrate, take 5 g per day, and you're good to go. If only all nutrition was that simple!

References

1. Mayhew DL, Mayhew JL, Ware JS. Effects of long-term creatine supplementation on liver and kidney functions in American college football players. Int J Sport Nutr Exerc Metab. 2002 Dec; 12(4): 453-60.
2. Schilling BK, Stone MH, Utter A, Kearney JT, Johnson M, Coglianese R, Smith L, O'Bryant HS, Fry AC, Starks M, Keith R, Stone ME. Creatine supplementation and health variables: a retrospective study. Med Sci Sports Exerc. 2001 Feb;33(2):183-8.
3. Tarnopolsky MA, Bourgeois JM, Snow R, Keys S, Roy BD, Kwiecien JM, Turnbull J. Histological assessment of intermediate- and long-term creatine monohydrate supplementation in mice and rats. Am J Physiol Regul Integr Comp Physiol. 2003 Oct; 285(4: R762-9.
4. Shefner JM, Cudkowicz ME, Schoenfeld D, Conrad T, Taft J, Chilton M, Urbinelli L, Qureshi M, Zhang H, Pestronk A, Caress J, Donofrio P, Sorenson E, Bradley W, Lomen-Hoerth C, Pioro E, Rezania K, Ross M, Pascuzzi R, Heiman-Patterson T, Tandan R, Mitsumoto H, Rothstein J, Smith-Palmer T, MacDonald D, Burke D; NEALS Consortium. A clinical trial of creatine in ALS. Neurology. 2004 Nov 9;63(9):1656-61.
5. Rosenfeld J, King RM, Jackson CE, Bedlack RS, Barohn RJ, Dick A, Phillips LH, Chapin J, Gelinas DF, Lou JS. Creatine monohydrate in ALS: effects on strength,fatigue, respiratory status and ALSFRS. Amyotroph Lateral Scler. 2008 Oct;9(5):266-72.
6. Groeneveld GJ, Veldink JH, van der Tweel I, Kalmijn S, Beijer C, de Visser M, Wokke JH, Franssen H, van den Berg LH. A randomized sequential trial of creatine in amyotrophic lateral sclerosis. Ann Neurol. 2003 Apr;53(4):437-45.
7. Neves M Jr, Gualano B, Roschel H, Lima FR, Lúcia de Sá-Pinto A, Seguro AC, Shimizu MH, Sapienza MT, Fuller R, Lancha AH Jr, Bonfá E. Effect of creatine supplementation on measured glomerular filtration rate in postmenopausal women. Appl Physiol Nutr Metab. 2011 Jun;36(3):419-22.
8. Cancela P, Ohanian C, Cuitiño E, Hackney AC. Creatine supplementation does not affect clinical health markers in football players. Br J Sports Med. 2008 Sep;42(9):731-5.
9. Gualano B, Ugrinowitsch C, Novaes RB, Artioli GG, Shimizu MH, Seguro AC, Harris RC, Lancha AH Jr. Effects of creatine supplementation on renal function: a randomized, double-blind, placebo-controlled clinical trial. Eur J Appl Physiol. 2008 May;103(1):33-40.
10. Candow DG, Chilibeck PD, Burke DG, Mueller KD, Lewis JD. Effect of different frequencies of creatine supplementation on muscle size and strength in young adults. J Strength Cond Res. 2011 Jul;25(7):1831-8.
11. Groeneveld GJ, Beijer C, Veldink JH, Kalmijn S, Wokke JH, van den Berg LH. Few adverse effects of long-term creatine supplementation in a placebo-controlled trial. Int J Sports Med. 2005 May;26(4):307-13.
12. Gualano B, de Salles Painelli V, Roschel H, Lugaresi R, Dorea E, Artioli GG, Lima FR, da Silva ME, Cunha MR, Seguro AC, Shimizu MH, Otaduy MC, Sapienza MT, da Costa Leite C, Bonfá E, Lancha Junior AH. Creatine supplementation does not impair kidney function in type 2 diabetic patients: a randomized, double-blind, placebo-controlled, clinical trial. Eur J Appl Physiol. 2011 May;111(5):749-56.
13. Taes YE, Delanghe JR, De Bacquer D, Langlois M, Stevens L, Geerolf I, Lameire NH, De Vriese AS. Creatine supplementation does not decrease total plasma homocysteine in chronic hemodialysis patients. Kidney Int. 2004 Dec;66(6):2422-8.
14. Taes YE, Delanghe JR, Wuyts B, van de Voorde J, Lameire NH. Creatine supplementation does not affect kidney function in an animal model with pre-existing renal failure. Nephrol Dial Transplant. 2003 Feb;18(2):258-64.
15. Taes YE, Delanghe JR, De Vriese AS, Rombaut R, Van Camp J, Lameire NH. Creatine supplementation decreases homocysteine in an animal model of uremia. Kidney Int. 2003 Oct;64(4):1331-7.
16. Gualano B, Ferreira DC, Sapienza MT, Seguro AC, Lancha AH Jr. Effect of short-term high-dose creatine supplementation on measured GFR in a young man with a single kidney. Am J Kidney Dis. 2010 Mar;55(3):e7-9.
17. Edmunds JW, Jayapalan S, DiMarco NM, Saboorian MH, Aukema HM. Creatine supplementation increases renal disease progression in Han:SPRD-cy rats. Am J Kidney Dis. 2001 Jan;37(1):73-78.
18. Pritchard NR, Kalra PA. Renal dysfunction accompanying oral creatine supplements. Lancet. 1998 Apr 25;351(9111):1252-3.