Creatine increases your body’s ability to produce energy during short, intense bursts of activity. It does this by replenishing the molecule your cells use as fuel, which translates into measurable gains in strength, power, and muscle size. But its effects extend beyond muscle. Creatine also plays a role in brain energy metabolism, influences how much water your muscles hold, and is one of the most thoroughly studied supplements in sports nutrition.
How Creatine Powers Your Cells
Every cell in your body runs on a molecule called ATP. When you lift a heavy weight, sprint, or do anything explosive, your muscles burn through their ATP supply within seconds. Creatine’s job is to recycle that fuel as fast as possible.
Here’s how it works: your body stores creatine in muscle tissue, where much of it bonds with a phosphate group to become phosphocreatine. When ATP gets used up and loses a phosphate group (becoming ADP), phosphocreatine donates its phosphate to rebuild ATP almost instantly. This reaction happens faster than any other energy system in your body, which is why creatine matters most during short, high-intensity efforts.
The process doesn’t stop there. Once phosphocreatine gives up its phosphate near the muscle fiber, the leftover creatine travels back to the mitochondria (your cell’s power plants), where it gets recharged into phosphocreatine again. This cycle, called the phosphocreatine shuttle, keeps energy flowing between where it’s produced and where it’s needed. Supplementing with creatine increases the total amount of phosphocreatine stored in your muscles, giving you a bigger energy buffer to draw from.
Effects on Strength and Muscle
The performance data on creatine is unusually clear. A review of 22 studies found that people who combined creatine supplementation with resistance training gained 20% more strength on average, compared to 12% for those training with a placebo. That’s an 8 percentage point advantage from supplementation alone. Weightlifting performance, measured as the number of reps someone could complete at a given percentage of their max, improved even more: 26% with creatine versus 12% without.
The range of individual responses is wide. Bench press improvements across studies ranged from 3% to 45%, which reflects differences in training experience, genetics, diet, and baseline creatine levels. People who start with lower creatine stores (vegetarians, for example) tend to see larger effects. The mechanism behind these gains is straightforward: more phosphocreatine means you can push out an extra rep or two per set, and over weeks of training, that additional volume adds up to more muscle growth.
What Happens to Your Weight
One of the first things you’ll notice after starting creatine is a bump on the scale. During the first week or two, most people gain 1 to 2 kilograms (roughly 2 to 4 pounds). This is water, not fat or muscle.
Creatine pulls water into your muscle cells, a process called cell volumization. The weight gain is intracellular, meaning the water moves inside the muscle fibers rather than pooling under your skin. For most people, this makes muscles look slightly fuller rather than bloated. After the initial water uptake stabilizes, any further weight gain over the following weeks typically reflects actual increases in lean tissue from training.
Effects on the Brain
Your brain consumes a disproportionate amount of energy relative to its size, and it relies on the same phosphocreatine system as your muscles. Creatine supplementation increases the brain’s energy reserves, reduces oxidative stress, and may support the production of key chemical messengers involved in learning and memory.
A systematic review and meta-analysis of clinical trials found that creatine supplementation produced a small but significant improvement in memory. It also reduced the time needed for attention-based tasks and improved processing speed. Interestingly, the cognitive benefits weren’t uniform across groups. Attention improvements were more pronounced in people with illnesses and in adults aged 18 to 60, with less effect seen in healthy individuals or those over 60. Processing speed improvements were significant in women but not in men. The review found no meaningful effect on overall executive function.
These brain effects are modest compared to the muscle and strength benefits, but they suggest creatine isn’t purely an athletic supplement.
How Your Body Makes Creatine Naturally
Your body produces creatine on its own, primarily through a two-step process involving the kidneys and liver. The kidneys create a precursor molecule from amino acids, and the liver finishes the job by adding a chemical group to produce creatine. The total pool of creatine and phosphocreatine in a 70-kilogram adult is about 120 grams. Each day, roughly 1.7% of that pool breaks down irreversibly into a waste product called creatinine, which your kidneys filter out through urine. That means you need to replace about 2 grams daily through a combination of internal production and food.
Dietary creatine comes almost exclusively from animal products, especially red meat and fish. A pound of raw beef contains roughly 1 to 2 grams. Supplementation is simply a way to top off your stores beyond what your body makes and what you eat.
Dosing: Loading vs. Maintenance
There are two common approaches. A loading phase involves taking 20 to 25 grams per day, split into smaller doses, for five to seven days. This saturates your muscle stores quickly. After that, a maintenance dose of 3 to 5 grams per day keeps levels topped off.
You can also skip the loading phase entirely and just take 3 to 5 grams daily from the start. This approach reaches the same saturation point, but it takes about three to four weeks instead of one. The end result is identical. The only difference is how fast you get there.
Side Effects and Stomach Issues
The most common complaints are gastrointestinal: bloating, cramps, nausea, or loose stools. These tend to happen during the loading phase, when you’re taking large doses at once. Creatine draws water into the intestines at high concentrations, which can cause stomach discomfort or diarrhea. Starting with a lower dose, skipping the loading phase, or using a micronized form that dissolves more easily in water can reduce these symptoms.
Muscle cramping has been reported anecdotally, but controlled studies haven’t consistently confirmed a direct link. Staying well hydrated while supplementing is a reasonable precaution, especially during intense training or hot weather.
Kidney Safety
This is probably the most common concern, and it stems from a misunderstanding about lab tests. Creatine naturally breaks down into creatinine, which is one of the markers doctors use to assess kidney function. Supplementing with creatine raises creatinine levels in your blood, which can make a kidney function test look abnormal even when your kidneys are perfectly fine.
Studies in healthy people have not found that creatine damages kidney function when taken at recommended doses. The Mayo Clinic notes it is likely safe for up to five years at standard doses. However, research in people with existing kidney disease is limited, so anyone with compromised kidney function should approach creatine differently and discuss it with their care team. If you’re getting bloodwork done while taking creatine, it’s worth mentioning your supplementation so your doctor can interpret the creatinine number in context.