Creatine: what the research does and doesn't show

Most searches about creatine and general health circle back to three things: does it make you gain weight, will it upset your stomach, and is it safe for a specific group — pregnant, breastfeeding, or under 18. The honest answers: yes to water weight (not fat), dose-dependent for stomach upset, and "talk to a doctor first" for every one of those specific groups, because none of them has been studied directly.

What the evidence doesn't support

It doesn't support fat gain — every study measuring body composition after creatine attributes the change on the scale to water and lean tissue, not fat mass. It doesn't include a dedicated trial isolating headaches as a creatine side effect, so there's no dose-response data to report on that question specifically. And it doesn't offer any dosing or safety guidance for pregnancy, breastfeeding or use under 18 — nobody runs a creatine trial in those groups, so a doctor's judgment fills the gap the research can't.

What the trials found

Weight: water and lean tissue, not fat

A one-week trial in 27 healthy adults gave a loading dose of creatine (0.3 g/kg body weight) or placebo, then measured body composition three separate ways. The creatine group's fat-free-mass reading rose 1.1-1.9 kg across all three methods, and total body water rose about 2% — changes the authors attribute to water retention, not new muscle or fat, given the one-week timeframe was too short for either. That's the best-documented number behind "how much water weight does creatine add," and no trial has tracked whether the effect changes with months of continued use rather than one week.

Over longer use, a meta-analysis of 35 randomized trials (1,192 adults) found creatine increased lean body mass by about 0.68 kg overall, but only when combined with resistance training — creatine paired with other exercise types, or with no exercise, showed no significant lean-mass effect. No trial in this literature measured fat mass increasing with creatine; the weight changes reported throughout this body of research are water and lean tissue.

Stomach upset: mostly about how much you take at once

A 28-day trial in 59 soccer players found diarrhea was the most common complaint in every group — including placebo (39% overall) — but showed up significantly more with a single 10 g dose (55.6%) than with the same 10 g split into two 5 g doses (28.6%) or placebo (35%). A separate 5-day trial found no gastrointestinal side effects at all in people taking creatine alone; mild GI discomfort appeared only in a subgroup combining creatine with caffeine (4 of 13 people). We didn't find a dedicated trial isolating constipation as a creatine effect — see does creatine cause diarrhea, bloating or gas? for the full breakdown, including bloating (which tracks with the water-retention finding above, not digestion).

Headaches: no dedicated trial found

We didn't find a trial that isolated headaches as a specific, measured outcome of creatine supplementation. The broadest safety analysis available — a 2025 pooled review of 685 clinical trials tracking 49 different side effects across roughly 26,000 combined participants — found no significant overall difference in side-effect frequency between creatine and placebo groups, but its published results don't break that out by headache specifically, so there's no headache-specific number to report here.

Questions people ask

Is it safe to take creatine during pregnancy or while breastfeeding?

This is a life-stage question the research on healthy adult supplement users doesn't answer, and it isn't one to work out from a supplement search. Talk to a doctor before taking creatine, or any supplement, during pregnancy or while breastfeeding.

Is creatine safe for teens?

There's limited dedicated research in people under 18, and our label's own directions are written for adults, with a note to consult a physician for anyone under 18. A 2021 expert position paper from the International Society of Sports Nutrition lists creatine's safety in children and adolescents as one of the field's still-open questions rather than a settled one — which is itself useful to know: researchers who study creatine for a living don't treat this as resolved. That's a reason for caution, not a dosing recommendation; a pediatrician is better positioned to weigh in for a specific teenager than any generic number would be.

Are creatine gummies as good as powder?

That's more of a label-reading question than a research one. Every trial on this page used creatine monohydrate as a powder or capsule at a specific gram dose — none tested a gummy formulation. If you're comparing a gummy product, check its serving size against the doses discussed on this site the same way you'd check a powder's; see how to choose a good creatine and creatine forms compared.

Does creatine cause weight gain if I'm trying to lose weight?

Any weight change creatine causes in the research above is water retention and, with resistance training, lean tissue — not fat. If you're tracking body fat specifically rather than the number on a scale, the trials in this literature don't report creatine adding fat mass.

When to talk to a doctor

Persistent gastrointestinal symptoms, frequent or severe headaches, any question during pregnancy or breastfeeding, or considering creatine for a child or teenager are conversations for a doctor, not something this page or a supplement label resolves. Creatine is not a treatment for a digestive condition, a headache disorder, or any diagnosed health issue. See who should not take creatine for who else should check first.

If you came here looking for creatine and a specific health condition, each has its own dedicated review rather than being folded into this page: anxiety, depression, ADHD, sleep, dementia, blood pressure, heart disease, diabetes, weight and obesity, liver health, and inflammation. For muscle cramps, menopause, or energy and focus specifically, see those reviews directly.