Cardarine (GW501516)

What it is

Cardarine is a synthetic molecule with the laboratory code GW501516, developed in the late 1990s by the pharmaceutical companies GlaxoSmithKline and Ligand. Unlike the SARMs it is often mentioned in the same breath with, Cardarine does not act on the androgen receptor but on a nuclear receptor called PPAR-delta. This is a sensor in the cell that switches genes for fat metabolism on and off.

The original aim was not a sports drug but a medicine for lipid metabolism disorders. The hope: more good HDL cholesterol, fewer triglycerides, without the side effects of the preparations available at the time. Only later did the substance become known through a study on endurance in mice and migrate from there into the training scene.

How it is supposed to work

PPAR-delta sits in muscle, fat and liver cells and controls there how many fatty acids are burned. If the receptor is activated with Cardarine, metabolism in cell and animal experiments shifts toward more fat burning, more HDL and fewer triglycerides. In humans this pathway has been directly demonstrated: in a study in overweight men, fat burning in muscle rose measurably, and the transport enzyme responsible for it was upregulated.

The famous endurance effect is more complicated than the advertising suggests. In the underlying 2008 paper, Cardarine alone did not increase running performance in untrained mice at all, only together with training. A later study found an effect even without training, but attributed it to the substance sparing glucose and thus keeping blood sugar up longer during running. That is an interesting principle, but from an animal model.

At the level of blood lipids, the chain of action in humans has by now been measured fairly well. In dyslipidemic men, Cardarine increased the breakdown of fat-carrying particles and the formation of the protective apolipoprotein A, a plausible pathway to more HDL and fewer triglycerides. This explains why the substance was originally intended as a cardiovascular medicine and not as a sports drug.

Where the reputation as a miracle drug comes from

The figure mentioned most often in forums is 44 percent more endurance. This figure comes from the 2008 mouse paper, but there it belongs to a different substance, the AMPK activator AICAR, not to Cardarine. For Cardarine, the same study reported 68 percent longer running time and 70 percent longer distance, and only in combination with four weeks of running training.

In this way, a drug candidate for fat metabolism became a symbol of performance without effort. What is usually missing in the marketing: the manufacturer never brought the substance to approval but abandoned development, and the reason was not a formal error but cancer in the animal studies.

What the studies show

Narkar et al., Cell 2008 - the endurance study

Male mice received Cardarine with or without four weeks of treadmill training. Without training, nothing happened to endurance, even though the oxidative genes were upregulated. Only together with training did running time rise by 68 and distance by 70 percent compared with trained control animals, and the proportion of enduring type I muscle fibers by around 38 percent. The much-cited 44 percent in the same paper belong to AICAR, not to Cardarine.

Olson et al., ATVB 2012 - the largest human study

In the largest controlled study in humans, 268 patients with low HDL received Cardarine or placebo over 12 weeks. HDL cholesterol rose by up to 16.9 percent, LDL fell by 7.3 percent, triglycerides by 16.9 percent and apolipoprotein B by 14.9 percent. Only blood lipid values were measured, no cardiovascular events and no performance data.

Gupta et al., Nat Med 2004 - the cancer signal

Mice with a hereditary predisposition to intestinal polyps were given the PPAR-delta ligand Cardarine. The number and size of the polyps increased markedly; the number of polyps larger than 2 millimeters rose fivefold. The role of PPAR-delta in colorectal cancer is not uniform in research, but this and other animal findings belong to the context of the cancer safety signals because of which development was stopped.

Where the data stop

The decisive gap: for endurance, fat loss or body composition in humans there is not a single study. All human data concern blood lipid values, that is, surrogate markers, and no study has tested hard endpoints such as heart attacks or mortality. Development was ended before such studies. The entire endurance reputation rests on mice, and even there Cardarine alone worked only to a limited extent.

The cancer signal, too, cannot be read in full detail in the public record. The statement that various types of cancer occurred in long-term animal studies comes from the notice of the manufacturer and the health authority, not from a detailed primary publication. Long-term data in humans are completely lacking, and no one knows how the substance acts over years.

Status, approval and legal

Cardarine is not approved as a medicine anywhere and is not a food supplement either. According to the manufacturer, clinical development was stopped in 2006. In sports the situation is clear: the 2026 WADA Prohibited List includes PPAR-delta agonists and names GW1516 and GW501516 explicitly, prohibited at all times, in and out of competition. In Germany, Cardarine is listed by name in the annex to the Anti-Doping Act, under the metabolic modulators, with the synonyms GW1516, Cardarin and Endurobol. As a result, acquisition, possession and bringing into the country of not insignificant quantities for the purpose of doping, as well as trading and supplying, are criminal offenses. We do not give dosage information.

Safety

The most important safety finding is the cancer signal from the long-term animal studies, because of which development ended. In addition, there is a published poisoning case: a man who had taken Cardarine together with the SARM ostarine developed severe liver cell damage and pronounced rhabdomyolysis with creatine kinase up to 86,435 units per liter, but recovered after six weeks. Combinations with other substances that strain the liver or muscles have not been studied. The substance is unsuitable for pregnant women and in the case of cancer risk or liver disease. Then there is the unreliable product quality from the gray market: in an analysis of products sold as SARMs, Cardarine turned up as an undeclared admixture, and only in about half of the products was the stated active substance correct at all.

Sources

• Narkar et al., Cell 2008
• Fan et al., Cell Metabolism 2017
• Oliver et al., PNAS 2001
• Sprecher et al., ATVB 2007
• Riserus et al., Diabetes 2008
• Olson et al., ATVB 2012
• Gupta et al., Nature Medicine 2004
• Kintz et al., Toxics 2021
• GSK and Health Canada, safety notice 2013
• WADA, Prohibited List 2026