Creatine side effects: what’s common and who should avoid it

What are the potential side effects of creatine?

Creatine is one of the most researched supplements, with studies lasting up to several years in healthy adults. The side effects that do show up are mostly mild and linked to the amount taken:

• Weight gain from water: creatine draws water into muscle cells. A gain of 1–2 kg in the first week or two is common, mainly with a loading phase. It is water in the muscle, not fat.
• Stomach upset: bloating, nausea or loose stools, mostly after large single doses of 10 g or more.
• Higher creatinine on blood tests: not a sign of damage in itself, but worth telling your doctor about (see below).

Can creatine make you bloated or cause diarrhoea?

It can, mainly at high doses. In one study of footballers, about 56% of those taking a single 10 g dose reported diarrhoea, compared with about 29% of those taking the same amount split into two 5 g doses. Splitting large loading doses, sticking to the usual daily amount, taking it with food and stirring the powder in well all help. Feeling “bloated” in the first weeks is often the water held in muscle rather than gut bloating.

Is creatine bad for your kidneys?

In healthy people, the research says no. A 2019 systematic review and meta-analysis concluded that creatine supplements did not cause kidney damage at the amounts and durations studied. Reviews by sports nutrition scientists reach the same conclusion for healthy adults at normal intakes, including over several years.

That does not apply to people who already have kidney disease, or a higher risk of it, such as people with diabetes or high blood pressure. There is not enough research in these groups, so speak to your GP or kidney team before taking creatine.

Why does creatine raise creatinine on blood tests?

Creatinine is the waste product your body makes when it breaks down creatine. Doctors use the level of creatinine in your blood to estimate how well your kidneys filter, a figure called eGFR. Taking creatine, eating a lot of meat or doing hard exercise before the test can all push creatinine up a little, so your eGFR can look lower than it really is.

Does creatine cause dehydration or cramps?

The evidence does not support this. The worry comes from the fact that creatine pulls water into muscles, but studies in athletes training in the heat have not found more cramps, muscle injuries or dehydration in people taking creatine, and some found fewer. Drinking enough during the day is sensible whether or not you take creatine.

Is creatine bad for your heart?

There is no good evidence that creatine at normal intakes harms the heart or raises blood pressure in healthy people. If you have a heart condition or take heart medicines, check with your GP or pharmacist first, as with any supplement.

Can creatine cause acne or headaches?

Acne is often blamed on creatine online, but there is no good research showing a link. Some people report headaches, especially in the first weeks; these are not well studied, and drinking enough water and avoiding large doses is the usual advice. If headaches persist, stop and speak to your GP.

Does creatine cause hair loss?

The worry comes from one small 2009 study that measured a hormone, not hair. A 2025 trial that measured hair directly found no difference. We cover the evidence in full in Does creatine cause hair loss?

Who should avoid taking creatine?

• People with kidney disease or reduced kidney function – speak to your doctor first.
• Under-18s – creatine supplements are not intended for children and teenagers.
• Pregnant or breastfeeding women – there is not enough research, so ask your GP or midwife.
• People taking regular medication – especially medicines that affect the kidneys, such as some diuretics, long-term high-dose anti-inflammatory painkillers or lithium; ask your pharmacist.
• People with a medical condition such as diabetes, high blood pressure or liver disease – check with your GP.

Is creatine safe for people over 50?

Much of the research in older adults has used 3–5 g a day for months at a time, alongside strength training, without safety problems in healthy participants. Older people are more likely to take medicines or have reduced kidney function without knowing it, so it is worth checking with your GP first, particularly if you have had a recent blood test showing reduced kidney function.

Why do some doctors not like creatine?

Most concerns come from three places: the creatinine effect on blood tests, which can look like a kidney problem; a few old case reports in people with existing kidney disease or taking other substances; and the fact that supplements are less tightly controlled than medicines. Many doctors and dietitians are comfortable with creatine for healthy adults – the key is to tell them you take it.

What should you never mix creatine with?

There are no known dangerous combinations with ordinary food and drink. Be careful about combining creatine with medicines that strain the kidneys, and ask a pharmacist if you take any regular medication. Heavy drinking works against both training and hydration. Avoid “stacked” products that combine creatine with stimulants, where you can’t easily see how much of each you are taking.

How can you lower the risk of side effects?

• Stick to the daily amount on the label – usually 3–5 g – and don’t take large single doses.
• Skip the loading phase if you want to avoid a quick jump on the scales.
• Take it with food if it upsets your stomach.
• Drink enough fluid through the day.
• Tell your doctor you take creatine before any blood test.

For the details on daily amounts and loading, see How much creatine per day.