Creatine monohydrate is the most researched ergogenic aid in sports science, and also the one most consistently discussed at the wrong altitude. The public conversation is about loading phases and bloating. The evidence base covers muscle saturation kinetics, a substantial baseline deficit in plant-based athletes, cerebral energy metabolism, sarcopenia in adults over 55, and a twenty-year sequence of failed attempts to improve on the molecule.
This is the whole picture in one place, with every study cited by PMID.
The Short Answer
| Question | Answer |
|---|---|
| Which form? | Creatine monohydrate. Nothing else has beaten it head-to-head. |
| Maintenance dose | 3–5 g/day, indefinitely |
| Loading dose | 20 g/day (4 × 5 g) for 5–7 days — optional |
| Time to full saturation | ~5–7 days with loading, ~28 days without |
| Does the endpoint differ? | No. Loading changes speed, not outcome. |
| Cycle off? | No |
| Kidney risk in healthy adults | None demonstrated |
| Largest responders | Vegetarians and vegans; adults over 55 |
Why Saturation Is the Whole Mechanism
About 95% of body creatine sits in skeletal muscle, most of it as phosphocreatine (PCr). PCr regenerates ATP faster than any other pathway in the body, which is why it dominates efforts lasting one to ten seconds — a heavy single, a 40-metre sprint, a repeated jump. When PCr runs down, power output falls with it.
An untrained, unsupplemented muscle sits at roughly 120–125 mmol/kg dry mass. The transporter-limited ceiling is around 160 mmol/kg. Supplementation is not adding a drug; it is filling a tank most people carry partly empty.
Harris and colleagues (1992) established the kinetics that every subsequent protocol rests on. Their work showed that repeated doses raise resting muscle total creatine substantially, that uptake is greatest in the first days of supplementation, and that muscles starting from a lower baseline take up the most. That last point turns out to matter enormously, and it is where most of the interesting population differences come from.
The ISSN position stand (Kreider et al., 2017) — still the most comprehensive synthesis available — grades the strength-and-power evidence at the highest level, alongside a safety review covering studies of up to five years.
Loading Versus Not Loading
The loading protocol saturates stores in five to seven days. Taking 3 g/day gets to the same place in about four weeks. The distinction is scheduling, not physiology.
| Approach | Time to saturation | GI effects | Week-one scale change | Use when |
|---|---|---|---|---|
| Load: 20 g/day × 5–7 d | 5–7 days | Moderate, dose-dependent | +1–2 kg water | Competition or training block inside two weeks |
| Gradual: 5 g/day | ~20 days | Minimal | +0.5–1 kg over 3 weeks | Default for most people |
| Gradual: 3 g/day | ~28 days | Minimal | +0.5–1 kg over 4 weeks | GI-sensitive; no deadline |
The week-one weight gain is intracellular water, not fat. Creatine enters muscle through the SLC6A8 transporter co-transported with sodium, raising intracellular osmolality and drawing water in with it. That is the mechanism working, not a side effect of it.
The Vegetarian Deficit
Creatine is present almost exclusively in animal muscle tissue.
| Food (raw) | Creatine (g/kg) |
|---|---|
| Herring | 6.5–10.0 |
| Pork | 5.0 |
| Salmon | 4.5 |
| Beef | 4.0–5.0 |
| Tuna | 4.0 |
| Chicken | 3.4 |
| Cod | 3.0 |
| Milk | 0.1 |
| All plant foods | ~0 |
Someone eating no meat or fish gets essentially none, leaving endogenous synthesis from arginine and glycine — about 1–2 g/day — as the only supply.
Burke and colleagues (2003) tested what that means in practice, comparing vegetarians and omnivores on an identical creatine and resistance-training protocol. The vegetarians showed the larger increases in muscle total creatine and in lean tissue. This is the clearest population-level demonstration of the principle in Harris's original kinetics: the further you start from the ceiling, the more supplementation does.
The practical consequence is that a plant-based athlete is not choosing between a small edge and nothing. They are correcting a measurable deficit against the competitors they race.
The Brain
Creatine's cerebral role is a genuinely separate literature from the muscle one, and a weaker one — but it is real.
The brain consumes roughly 20% of resting energy expenditure on 2% of body mass, and PCr buffers neuronal ATP the same way it buffers muscular ATP. The complication is that creatine crosses the blood-brain barrier inefficiently; the brain relies substantially on its own synthesis via the AGAT and GAMT enzymes.
Dechent and colleagues (1999) settled whether oral supplementation reaches the brain at all, using MR spectroscopy to measure a roughly 9% increase in total brain creatine after four weeks. Small, but measurable and reproducible.
The functional effects appear where the baseline is lowest or the demand is highest — the same pattern as in muscle:
- Low baseline. Rae and colleagues (2003) randomised vegetarians to 5 g/day or placebo and found significant improvements in working memory and processing speed.
- High demand. McMorris and colleagues (2006) found that creatine attenuated the decline in cognitive and psychomotor performance produced by sleep deprivation.
- Injury. Sakellaris and colleagues (2006) ran an open-label randomised trial of creatine in children and adolescents with traumatic brain injury and reported reductions in complication rates, including duration of post-traumatic amnesia and intensive care stay.
Adults Over 55
This is arguably the strongest evidence in the entire creatine literature, and it is the one the supplement's marketing ignores.
Muscle mass declines roughly 3–5% per decade after 30 and accelerates after 60. Type II fast-twitch motor units are lost preferentially, and resting intramuscular PCr declines with age — which means the ageing muscle loses capacity in precisely the energy system creatine supports.
Gualano and colleagues (2014) ran a randomised, double-blind, placebo-controlled trial of creatine plus resistance training in vulnerable older women and found greater gains than resistance training alone, with no adverse effect on renal function in that age group.
Devries and Phillips (2014) settled the question at the level of the whole literature with a meta-analysis of creatine during resistance training in older adults, concluding that supplementation produces greater increases in lean mass and strength than resistance training by itself.
For this population the protocol is simpler than for athletes: skip loading entirely. Take 3–5 g/day, reach full saturation in three to four weeks, and avoid the gastrointestinal discomfort that makes people abandon the supplement in week one.
Women
Creatine research was performed overwhelmingly on men for three decades, and the resulting cultural framing — a supplement for male strength athletes — is not supported by the data.
Smith-Ryan and colleagues (2021) reviewed creatine across the female lifespan in *Nutrients*. Women have lower endogenous creatine stores than men, partly from lower habitual dietary intake, and the review found the strongest case for supplementation in peri- and post-menopausal women, where creatine combined with resistance training supports lean mass and skeletal outcomes during a period of accelerated loss.
Two practical points follow. First, there is no evidence supporting a reduced dose for women — the 3 g/day sometimes recommended has no pharmacokinetic basis, and the standard 3–5 g/day applies. Second, the initial 1–2 kg is intracellular water, which matters for weight-class athletes as a timing consideration and for nobody else.
Every Attempt to Improve on Monohydrate
The supplement industry has tried to replace creatine monohydrate repeatedly: ethyl ester, buffered forms, citrate, malate, liquid, time-release. Each launched on a bioavailability claim. None has beaten monohydrate in a head-to-head trial.
Creatine ethyl ester had the most plausible rationale — esterification to improve membrane permeability. Spillane and colleagues (2009) tested it directly against monohydrate over 48 days of resistance training with serum and muscle creatine measurement. The ethyl ester group finished with significantly lower muscle creatine than the monohydrate group. The ester bond is cleaved to creatinine before absorption, so the product delivers the waste metabolite rather than the compound.
The general point is mechanical. Intestinal uptake is governed by the SLC6A8 transporter, which has a finite transport capacity. Improving solubility or gastric stability does not raise that ceiling, which is why more soluble forms such as citrate and malate do not outperform monohydrate at matched creatine content. The ISSN position stand states the conclusion plainly: no alternative form has demonstrated a superior ergogenic effect.
Micronised monohydrate is the one worthwhile refinement — identical molecule, finer particle size, mixes better. Buy that, and disregard the rest.
Heat and Hydration
Creatine loading increases total body water by roughly 1–2 litres, most of it intracellular. The proposed thermoregulatory logic is that a larger intracellular water mass buffers metabolic heat and helps defend plasma volume during prolonged work in heat.
The direct evidence here is thinner than the muscle literature and deserves stating carefully. Beis and colleagues (2011) examined creatine and glycerol hyperhydration in well-trained endurance runners, measuring effects on running economy. It is a hyperhydration study, and it does not establish that creatine alone lowers core temperature during exercise in heat — a claim frequently attributed to it.
The defensible practical position: creatine loading raises total body water, and that shift is only useful in an athlete who is drinking enough to support it. Loading while under-hydrated moves fluid inward without replacement. Creatine is not a substitute for fluid intake or heat acclimatisation, and should not be adopted for thermoregulation on the current evidence.
Safety, and the Creatinine Confusion
Kreider and colleagues (2017) reviewed the safety literature in the ISSN position stand and found no evidence of renal harm from 3–5 g/day in healthy individuals, including in studies extending to five years. Antonio and colleagues (2021) addressed the recurring misconceptions directly in a dedicated review.
One point causes more unnecessary alarm than the rest. Creatine supplementation raises serum creatinine, and serum creatinine is used clinically to estimate kidney function. The rise reflects increased creatine turnover, not renal injury — but it will show up on a routine blood panel and can be misread as declining kidney function by anyone unaware the patient supplements. Mention it before the test, not after.
People with existing renal disease should take medical advice before supplementing. That caveat is real, and it is not a reason for healthy adults to avoid the supplement.
What to Actually Do
1. Buy micronised creatine monohydrate. Ignore every other form and every premium price attached to one. 2. Take 3–5 g/day, every day. Timing is a rounding error next to consistency. 3. Skip loading unless a competition or training block starts within two weeks. You reach the same saturation either way. 4. If you are vegetarian or vegan, treat this as a priority, not an optimisation. Your baseline is the reason the effect will be larger. 5. If you are over 55, this is a sarcopenia intervention as much as a performance one — and it only works alongside resistance training. 6. Do not cycle off. There is nothing to recover from.