Cardarine (GW-501516) is a PPAR-delta agonist developed by GlaxoSmithKline for cholesterol and metabolic disease. It improved endurance dramatically in mice, but development stopped in 2007 after animal studies showed cancers developing in multiple organs. The World Anti-Doping Agency took the rare step of warning athletes directly about it.
- It is not a SARM and does not affect testosterone.
- Small human trials showed better cholesterol and fat metabolism over a few weeks.
- The long-term cancer risk in people is unknown and is the central concern.
Cardarine has a big reputation for cardio and fat loss. It also has one of the most serious red flags of any compound sold as a research chemical. This guide covers both sides.
What Cardarine is
GW-501516 activates PPAR-delta (peroxisome proliferator-activated receptor delta), a protein that switches on genes for burning fat and building mitochondria, especially in muscle. It was developed in the 1990s by Ligand Pharmaceuticals and GlaxoSmithKline as a potential treatment for high cholesterol, obesity and diabetes.
The “exercise in a pill” studies
In a widely publicised 2008 study in the journal Cell, researchers at the Salk Institute found that GW-501516 combined with exercise greatly increased running endurance in mice, and that a related drug, AICAR, improved endurance even in sedentary mice. Muscles shifted towards fat-burning, fatigue-resistant fibres. Headlines followed, and so did interest from athletes.
What human studies showed
A handful of small phase 1 and 2 trials gave GW-501516 to people for two to twelve weeks:
- HDL cholesterol rose and triglycerides and LDL fell.
- Fat burning in muscle increased and liver fat decreased in a short study of men with mild obesity.
- Insulin sensitivity improved in some measures.
Why development stopped
In 2007, GlaxoSmithKline halted development after long-term animal studies found that mice and rats given GW-501516 developed cancers in many organs, including the liver, bladder, stomach, skin, thyroid and tongue, at doses that, adjusted for body size, were not far from those discussed for people. In 2013 the World Anti-Doping Agency issued an unusual public alert warning athletes that the compound had never been approved and had serious toxicity concerns.
Whether the same risk applies to humans at shorter durations is unknown. That uncertainty is the problem: no one can say how much exposure, if any, is safe.
Other considerations
- It is not a SARM and does not suppress testosterone.
- It does not build muscle directly.
- Some users report better cardio and fat loss; there are no controlled human data on performance.
- Product quality varies; it is also found as an unlisted ingredient in some products sold as SARMs.
Sport
GW-501516 is banned at all times under the World Anti-Doping Agency code. Cyclists and other endurance athletes have received suspensions for it, and its metabolites can be detected for weeks.
Safer ways to build endurance
The changes Cardarine produced in mice, more mitochondria and better fat oxidation, are the main adaptations to aerobic training. Consistent low-intensity cardio, a weekly interval session, enough sleep and good fuelling deliver them without the unknowns. See HIIT workouts, cycling for fat loss and our article on SR9009, another compound marketed for endurance.
Why the cancer finding matters so much
Many drugs cause problems in animals at very high doses that never appear in people. What made the GW-501516 findings stand out was that tumours appeared in many different organs, in more than one species, and at doses that were not hugely above those used in human trials. PPAR-delta is involved in cell growth and survival, which gives a plausible reason the effect could matter in humans too. Regulators and drug companies treat that combination very seriously, which is why development stopped rather than continuing with warnings. Without long-term human data, nobody can rule the risk in or out.
Bloodwork if used
A lipid panel, liver enzymes, fasting glucose and a complete blood count are sensible baselines. They will not detect cancer risk. Arrange tests through your doctor or privately at LifeLabs or Dynacare; see our bloodwork guide.
Products and legal status
We carry Zionova Cardarine GW-501516 and Genetix GW-501516 for research, with batch lab results on each product page. GW-501516 is not authorised by Health Canada for human use.
Frequently asked questions
Why was Cardarine discontinued?
GlaxoSmithKline stopped development in 2007 after long-term animal studies showed cancers developing in multiple organs.
Is Cardarine a SARM?
No. It is a PPAR-delta agonist. It does not act on the androgen receptor or suppress testosterone.
What did human studies of Cardarine show?
Short trials at 2.5–10 mg a day improved cholesterol and fat metabolism. None studied long-term safety or performance.
Photo: Quino Al, StockSnap (public domain).
General information about a research compound, not medical advice. GW-501516 is not approved for human use in Canada.
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