First, the boring good news
Here’s a surprising number. Of 656 creatine studies, only 58 were done in women alone.1 One team gathered the 29 that tracked side effects: 951 women, aged 16 to 67, on 1 to 30 g a day for up to a year. Nothing serious happened to anyone, and stomach, kidney and liver problems were no more common than on a dummy powder.1
The longest study in women followed 237 women after menopause on about 10 g a day for two years. Stomach complaints: 13 on creatine, 17 on the dummy powder. Muscle cramps: 2 and 2.2 If you were hoping for drama, this is not your supplement.
So what does happen? Mostly three things.
1. The scale goes up a little (mostly water)
The one side effect that keeps showing up is weight gain, about 1 to 2 kg (about 2 to 4 lb) in the first month of strength-training studies.1213 In the women’s studies, it wasn’t even a real difference from the dummy powder.1 The water goes into your muscle cells, which is where you want it. Our piece on water weight has the details.
2. Your stomach cares about one dose, not the daily total
In 59 top soccer players (men, sadly), one group took 10 g at once, one took two 5 g doses, and one took a dummy powder, for 28 days. Who got diarrhea?3
Who got diarrhea in 28 days
Same daily amount, taken in one go or split in two
Elite soccer players, all men. Source3
Yes, the dummy-powder group too, which says a lot about heavy training and team buffets. Splitting the dose brought the rate back to dummy-powder level.3 The likely reason: with one big dose, some creatine stays in your gut and pulls water in with it.4
The simple fixKeep each serving at 5 g or less. If you're loading, split it into several doses through the day.
3. The kidney blood test that can fool your doctor
This one really trips women up. Your body turns creatine into a waste product called creatinine, and creatinine is exactly what the standard kidney blood test measures. So on creatine, the kidney score on that test can look worse, even when your kidneys are fine.
A big review of 26 trials showed this clearly. On creatine, the kidney score on the standard blood test dropped by about 11 points. But when kidney function was measured directly, it didn’t drop at all.6 The test changed. The kidneys didn’t.
In women after menopause, a direct kidney test stayed flat for 12 weeks on creatine.5 The 2024 international kidney guideline now lists creatine as a reason the standard test can be off, and points to cystatin C, a different kidney test your doctor can order.7 In one case report, creatine made a man’s results look like advanced kidney failure. His kidneys were fine.14
Your kidneys can be completely fine while your lab report says otherwise. Tell your doctor you take creatine before the blood draw.
If you already have kidney disease, there’s not much research, and the American Kidney Fund and Mayo Clinic both say to talk to your doctor first.1516
Cramps, dehydration and your liver: the myths
Cramps and dehydration. These worries come mostly from old surveys of athletes, many taking more than the usual dose along with other supplements.17 A review of 10 proper trials found no sign that creatine hurts how you handle heat or hold on to fluid.18 College football players on creatine, training in heat up to about 99 °F (37 °C), had less cramping than players who weren’t.19 Plot twist: in a small study of people on kidney dialysis, creatine cut cramps by 60%.20
Liver. In the women’s studies, liver tests matched the dummy powder.1 In the two-year study, small liver-enzyme rises showed up in 6 women on creatine and 3 on the dummy powder, all mild.2 The NIH’s database of things that can injure the liver doesn’t even have an entry for creatine.21
Hormones, acne and the questions nobody has studied
Short answer: nobody has studied these properly yet.
- Female hormones: no proper trial has measured them on creatine. One small study of 15 women around and after menopause, with no comparison group, found no real change in estradiol (the main form of estrogen) over 14 weeks.22
- Acne: never tested. A 2026 skin review found no studies at all on creatine you swallow and your skin.23 In 8 teens on the acne drug isotretinoin, supplements (protein, creatine or herbal) were the likely cause of raised liver enzymes.24 If you’re on it, tell your dermatologist everything you take.
- Hair: the worry about DHT, a hormone tied to hair loss, comes from one study in young men. Our hair-loss piece covers it.
Who should talk to a doctor first
| If this is you | Why |
|---|---|
| Kidney disease | Not much research, and the standard kidney test gets harder to read715 |
| Pregnancy | Not tested in pregnant women yet; a first dosing study has been registered825 |
| Breastfeeding | Nobody has measured how much reaches breast milk; a US government database says "probably best to avoid" unless prescribed9 |
| Bipolar disorder | In two small studies, 4 of 19 people tipped into mania or a milder form of it1011 |
| Isotretinoin or other drugs that strain the liver | Supplements were linked to raised liver enzymes in teens24 |
One more: in people with Parkinson’s disease taking creatine, more caffeine was linked to the disease getting worse faster.26 A very specific group, and a link isn’t proof. But it’s why Mayo Clinic lists caffeine as a possible interaction.16
The side effect nobody talks about: no creatine at all
In a 2025 lab test run by the supplement industry, 4 of 6 best-selling creatine gummies failed. Two had no creatine the lab could detect, and two had only traces. All 5 powders passed.27 Outside scientists didn’t review it, so call it a warning, not a verdict.
Older lab work also found unwanted compounds in some creatine products.28 The practical move: a plain powder that says “creatine monohydrate” on the label, with an independent testing seal like NSF, USP or Informed Choice.15