Cardarine (GW-501516)

Overview

Cardarine (development code GW-501516, also GW1516, GSK-516, or "Endurobol") is a synthetic small-molecule selective agonist of the peroxisome proliferator-activated receptor delta (PPARδ, also called PPARβ/δ). It is NOT a peptide — it is a lab-made chemical that switches on a nuclear receptor. It appears on this peptide reference because it is frequently discussed and stacked alongside peptides in the fitness and "research chemical" community, not because it is one.

GW-501516 was developed in the 1990s by Ligand Pharmaceuticals and GlaxoSmithKline (GSK) as a candidate for dyslipidemia and metabolic disease. It became widely known after a 2008 mouse study (Narkar et al., Cell) reported that, combined with exercise, it sharply increased running endurance — earning it the "exercise mimetic" and "Endurobol" labels. Human testing never went beyond a small number of short lipid trials.

Chemistry and structure

Cardarine is a small-molecule thiazole-containing compound, not an amino-acid chain.

Mechanism of action

• PPARδ (PPARβ/δ) nuclear receptor. Cardarine is a high-affinity, selective agonist reported at roughly 1,000-fold selectivity over PPARα and PPARγ. The activated receptor pairs (heterodimerizes) with RXR and drives transcription of genes for fatty-acid uptake, β-oxidation, and mitochondrial function. [In vitro]
• Skeletal-muscle oxidative metabolism. In animals it increases the oxidative (type I) myofiber gene program and fatty-acid oxidation, and synergizes with AMPK activation and exercise training to increase running endurance — the basis for the "exercise mimetic" label. [Animal]
• Lipid / lipoprotein metabolism. In short human trials it raised HDL cholesterol and apoA-I and lowered LDL, triglycerides, apoB, and free fatty acids. [Human]
• Tumor promotion. Long-term high-dose dosing promoted rapid multi-organ tumor formation in rodents — the reason development was abandoned. PPARδ activation in proliferating cells raises a mechanistic carcinogenicity concern. [Animal]

Research and evidence

Human evidence in context. Human data are limited to a small number of short (roughly 2–12 week) Phase 1/2 lipid trials. They showed favorable short-term HDL/LDL/triglyceride changes but produced no long-term outcome data and no long-term safety data. There are no human studies of endurance performance, body composition, or fat loss that establish the "exercise mimetic" effect in people — that claim rests on animal work. Human bioavailability, half-life, and pharmacokinetics were not found in these sources.

Status and regulation

• Regulatory approval: None. GW-501516 is not approved by the FDA, the EMA, or any other regulator for any indication. GlaxoSmithKline discontinued development around 2007 following the rodent carcinogenicity findings. (The exact internal GSK decision details come from secondary sources.)
• Anti-doping: Prohibited by the World Anti-Doping Agency (WADA) since 2009, listed under Metabolic Modulators (S4.5) and prohibited at all times (in- and out-of-competition), per USADA and Sport Integrity Australia summaries. The exact current-year class code is confirmed via those anti-doping summaries rather than read directly from the official WADA Prohibited List PDF.
• Market reality: It is sold only as a "research chemical" and circulates on the black market despite the unresolved cancer risk. Such products are of unknown identity, purity, and potency.

Safety

Beyond the cancer signal, human safety information is thin: only short lipid trials were conducted, and their duration is far too limited to characterize real-world risk. Any product sold as "cardarine" is unregulated, so contamination, mislabeling, and incorrect dosing are additional, separate hazards.

Legal status

How it compares

Cardarine is often grouped with metabolic and "mitochondrial/endurance" compounds, but the honest comparison is that most of those are peptides with their own (also limited) evidence, while Cardarine is a small-molecule receptor agonist with an unresolved cancer signal:

• MOTS-c — a mitochondrial-derived peptide studied for exercise and metabolic effects. Unlike Cardarine, it is a peptide; both are early-evidence and neither is an approved performance drug.
• Retatrutide — an investigational metabolic/weight-loss peptide with peer-reviewed human trials. It shares the "metabolic" theme but is a distinct molecule class and is not carcinogenicity-flagged the way Cardarine is.

The decisive difference: Cardarine's development was stopped over rodent cancer findings and it has no approved use — it is not a benchmarked, evidence-backed therapy. See the Weight management overview.

Common misconceptions

• "Cardarine is a SARM." No. SARMs act on the androgen receptor; Cardarine is a PPARδ agonist. It is frequently sold alongside SARMs, which is the source of the confusion.
• "Cardarine is a peptide." No. It is a synthetic small molecule (C21H18F3NO3S2, 453.5 g/mol). It is covered here only because it is discussed and stacked with peptides.
• "It's non-hormonal, so it's safe." Not established. Being non-hormonal says nothing about carcinogenicity — and the rodent multi-organ tumor signal is exactly why the drug was abandoned.
• "Human trials proved it boosts endurance." No. The endurance ("exercise mimetic") data are from mice. Human trials only measured lipids, over short periods.

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This entry is educational and summarizes published research and public regulatory information. It is not medical advice, a recommendation, or a guide to obtaining or using any substance.