History

GW-501516 was developed in the 1990s-2000s through a GlaxoSmithKline/Ligand collaboration as a candidate treatment for dyslipidemia and metabolic disease. It is a potent, selective PPARδ agonist with reported low-nanomolar affinity. Development was terminated around 2007 after long-term rodent carcinogenicity studies showed tumors in multiple organs — a finding corroborated by USADA and Sport Integrity Australia. It was never approved for human or veterinary use by any regulatory authority.

Cardarine (GW-501516) is frequently sold and discussed alongside SARMs in the “research chemical” market, but it belongs to a different class entirely: it is a synthetic PPARδ agonist, not a peptide and not a SARM. It generated early interest as an “exercise mimetic” because activating PPARδ in muscle upregulates fatty-acid oxidation and mitochondrial metabolism. However, its development was abandoned after long-term animal studies found cancer in multiple organs, and no human trials have ever tested it for athletic performance, fat loss, or long-term safety.

What it is

GW-501516 (also called GW1516, Endurobol, or Cardarine) is a small-molecule synthetic compound that activates PPARδ (peroxisome proliferator-activated receptor delta). It is not a peptide and not a SARM — SARMs act on the androgen receptor, which GW-501516 does not. Because it is often grouped with SARMs in the unregulated research-chemical market, its class is widely misunderstood. Activating PPARδ in muscle increases expression of genes governing fatty-acid oxidation and oxidative metabolism, which is the biological basis for the “exercise in a pill” framing. It was developed as a candidate for dyslipidemia and metabolic disease and was never approved for any use.

The claims

Marketers and users claim Cardarine delivers endurance enhancement (“exercise in a pill”), fat loss, improved running and stamina, and favorable lipid changes such as raised HDL and lowered triglycerides. It is sold online as a “research chemical” or falsely presented as a supplement ingredient.

What the evidence actually shows

Human data are limited to short metabolic trials. There are no human trials for athletic performance, fat loss, or long-term safety.

Healthy-volunteer trial (Sprecher et al., 2007): The first report of a PPARδ agonist in humans. Healthy sedentary men received placebo or GW-501516 for two weeks. Triglycerides trended down and post-fat-meal triglyceride clearance improved. The cohort was small, short-duration, and sedentary.
Low-HDL patient trial (Olson, Pearce, Jones, Sprecher, 2012): A randomized placebo-controlled trial (n=268) in subjects with low HDL. At the top dose, GW-501516 raised HDL-C by up to ~~16.9% and lowered triglycerides (~~-16.9%), LDL (~~-7.3%), apoB (~~-14.9%), and free fatty acids. This is the largest human dataset, but it was still short and reported lipid endpoints only — no cardiovascular outcome data.
Animal endurance evidence: The widely cited “exercise mimetic” finding (PPARδ agonism plus training increasing running endurance) comes from mouse studies (Narkar et al., Cell 2008). This has not been replicated in humans.

There is biological plausibility and rodent endurance data, but human performance and fat-loss benefit are unproven, and development was halted before efficacy could be established in people.

Legal and regulatory status

United States (FDA): GW-501516 has no approved use. SARMs and SARM-adjacent research chemicals sold as supplements are not lawful dietary-supplement ingredients — the FDA’s position is that they are unapproved drugs that do not comply with DSHEA. The FDA issued warning letters in 2017 and a consumer warning citing risks including liver damage, heart attack, and stroke for the broader SARM category.

DEA scheduling: GW-501516 is not a federally scheduled controlled substance in the US. A “SARMs Control Act” has been proposed in past Congressional sessions to schedule certain SARMs, but GW-501516 is not DEA-scheduled — and, being a PPARδ agonist rather than a SARM, it would not necessarily fall under such an act regardless. (For comparison, oxandrolone is a distinct, FDA-approved anabolic-androgenic steroid and a Schedule III controlled substance under the Anabolic Steroid Control Act; it is unrelated to GW-501516.)

Australia: GW-501516 is classified as a poison/prohibited substance.

Anti-doping (WADA): GW-501516 (GW1516) is prohibited at all times — in- and out-of-competition — under Section S4.5 “Metabolic Modulators” (within S4, Hormone and Metabolic Modulators), which covers PPARδ agonists and the PPARδ-AMPK axis. WADA added it to the Prohibited List in 2009 after developing a detection test. SARMs (ostarine, andarine, LGD-4033, RAD140, and others) are prohibited under a separate class, S1.2 “Other Anabolic Agents.” USADA has cited 31 worldwide sanctions for GW-501516 detection in 2017 alone.

Safety

Carcinogenicity is the headline harm. GSK/Ligand terminated development around 2007 because long-term rodent carcinogenicity studies showed tumors in multiple organs — confirmed by USADA and Sport Integrity Australia. The full mouse two-year carcinogenicity study is most reliably described as toxicology work presented in conference/abstract form rather than a definitive peer-reviewed article, but the carcinogenicity outcome itself is well corroborated by multiple independent anti-doping and review sources. This is the single most important safety signal: a known multi-organ cancer finding at the dose levels and durations needed for chronic use. WADA and USADA have issued formal safety alerts warning athletes and consumers against GW-501516 specifically because of this cancer risk.

Hormonal effects: GW-501516 is a metabolic modulator, not a hormone, and is not established to cause testosterone suppression the way SARMs and anabolics do. Testosterone suppression, HDL reduction, and hepatotoxicity are documented concerns for SARMs (a different class) — those harms should not be attributed to GW-501516.

A note on vision claims: The yellow-tinted vision and night-vision difficulty widely reported online belong to andarine (S-4), a SARM, and are attributed to its action on retinal tissue. This is a property of andarine, not GW-501516, and is included here only as a contrast point.

Quality risk: Products sold as “Cardarine” are unregulated, and analyses have found mislabeling, wrong compounds, and contamination.

There is no verifiable published finding of QT prolongation or blindness attributable to GW-501516 itself; such claims are omitted here rather than repeated.

Bottom line

Cardarine (GW-501516) has preliminary human data showing favorable short-term lipid effects, and rodent data suggesting endurance benefits — but no human evidence for performance, fat loss, or long-term safety. Most importantly, its development was abandoned because long-term animal studies found cancer in multiple organs. It has no approved human use, is sold only as an unregulated research chemical, and is banned in sport at all times. The proven carcinogenicity signal in animals is the decisive reason for caution.

Evidence grade: Preliminary human.