Cardarine — GW-501516, sometimes sold as endurobol — is the compound behind the “exercise in a pill” headline. It is also one of the most consistently miscategorised substances in the performance market: it sits on the same vendor pages as ostarine and RAD-140, it is described in the same breath as them, and it is not a SARM. It never was. The other thing the vendor pages leave out is why you can buy it from a research-chemical site but not from a pharmacy: GlaxoSmithKline stopped developing it after long-term rodent studies produced tumours, and no company has taken it forward since. Both facts are load-bearing, and both are documented. Here is the whole record.
That meter is specifically about endurance, because that is what cardarine is bought for. The lipid programme is a separate story and it did reach Phase 2 in humans before it was abandoned — we cover exactly what those trials found below.
The correction that matters most: cardarine is not a SARM
SARMs — selective androgen receptor modulators — do what the name says: they bind the androgen receptor, the same receptor testosterone uses, with the goal of driving muscle growth in some tissues while sparing others. Ostarine, RAD-140 and LGD-4033 all work this way. We break that class down separately in peptides vs SARMs.
Cardarine does none of that. It was developed at GlaxoSmithKline using combinatorial chemistry and structure-based drug design as a potent, subtype-selective agonist of PPARδ — peroxisome proliferator-activated receptor delta, a nuclear receptor that acts as a dietary lipid sensor and switches on genes for fatty-acid handling.[1] In the founding 2001 paper it raised expression of the reverse cholesterol transporter ABCA1 and, in insulin-resistant obese rhesus monkeys, produced a dose-dependent rise in HDL cholesterol with falls in small dense LDL, triglycerides and fasting insulin.[1] Androgen receptor: not involved, not targeted, not implicated.
This is not a pedantic distinction. It changes what you should expect and what you should worry about. Cardarine will not suppress your own testosterone the way a SARM can, because it never touches that axis. It also will not build muscle through that axis. And its actual risk profile — which is the reason it exists only as a research chemical — comes from a completely different place than a SARM’s.
| Cardarine (GW-501516) | SARMs (ostarine, RAD-140, LGD-4033) | |
|---|---|---|
| Receptor | PPARδ — a nuclear lipid-sensing receptor | Androgen receptor — testosterone's receptor |
| Drug class | Metabolic modulator / PPARδ agonist | Non-steroidal androgen receptor modulator |
| Primary intended effect | Shift fuel use toward fatty-acid oxidation; raise HDL, lower triglycerides | Increase lean mass and strength via androgenic signalling |
| Effect on natural testosterone | No androgen-receptor activity, so no direct suppression of the HPG axis | Suppression of endogenous testosterone is a recognised class effect |
| What ended / limits development | Two-year rodent carcinogenicity findings; programme discontinued | Liver injury and cardiovascular signals; no SARM is FDA-approved either |
| WADA status | Prohibited at all times under S4, hormone and metabolic modulators | Prohibited at all times under S1, anabolic agents |
“Exercise in a pill” — what the rodent work actually showed
The claim traces to one famous paper: Narkar and colleagues, in Cell in 2008, testing pathway-specific drugs on treadmill endurance in mice.[2] It is worth reading the finding precisely, because the popular version has drifted a long way from it.
What the paper reported is that the PPARβ/δ agonist and exercise training synergistically increased oxidative myofibres and running endurance in adult mice. The drug amplified training. It did not substitute for it. The result everyone quotes — sedentary animals running 44% further with no training at all — came from the other arm of the same study, four weeks of AICAR, an orally active AMPK agonist. AICAR is a different molecule with a different mechanism. Attributing its sedentary-mouse result to cardarine is the single most common error in writing about this compound.[2]
The underlying biology is nonetheless coherent: PPARδ activation upregulates the machinery of fatty-acid oxidation in skeletal muscle, remodels fibre type toward oxidative slow-twitch, and overlaps substantially with the transcriptional response to endurance training — which is exactly why the “exercise pill” literature keeps returning to this receptor.[3] It is a real target. The gap is between a target and a drug. For a newer compound making a very similar promise from a different receptor, and running into a very similar evidence gap, see SLU-PP-332.
What was actually tested in humans
Cardarine did get into people — hundreds of them — and the trials were competently done and published in real journals. None of them was about endurance.
- First-in-human, 2007. Twenty-four healthy volunteers, hospitalised and deliberately sedentary, given placebo (n=6), 2.5 mg (n=9) or 10 mg (n=9) daily for two weeks. HDL cholesterol rose in both drug groups while falling 11.5% in placebo; triglycerides trended down at 10 mg and post-fat-meal triglyceride clearance improved.[4] Note the design: the very first human study removed exercise on purpose.
- Metabolic syndrome, 2008. Six moderately overweight men per arm, 10 mg daily for two weeks against a PPARα comparator and placebo. GW-501516 cut fasting triglycerides 30%, apolipoprotein B 26%, LDL cholesterol 23% and insulin 11%, reduced liver fat 20% and urinary isoprostanes (a global oxidative-stress marker) 30%, and increased skeletal-muscle CPT1b expression — direct evidence the fat-oxidation mechanism operates in humans.[5]
- The largest trial, 12 weeks. 268 patients with low HDL cholesterol randomised to 2.5, 5.0 or 10.0 mg or placebo. HDL cholesterol rose up to 16.9% and apoA-I 6.6%; LDL cholesterol fell 7.3%, triglycerides 16.9%, apoB 14.9% and free fatty acids 19.4%. A smaller companion study (n=37) showed fewer VLDL and IDL particles and more medium and large HDL particles.[6] This is the high-water mark of the human evidence, and it is a lipid result.
- Mechanism in dyslipidaemic men, 2011. Thirteen men with central obesity, randomised double-blind crossover, 2.5 mg/day for six weeks. Stable-isotope kinetics showed the triglyceride effect came from faster VLDL clearance and lower apoC-III production, and the HDL effect from increased apoA-II production.[7]
Add it up: the longest human exposure on record is twelve weeks, the population was dyslipidaemic or metabolically unhealthy adults, and every primary endpoint was a lipid or a lipoprotein. That is a legitimate Phase 2 signal for a cardiometabolic drug. It is not evidence about athletic performance, and it is not long-term safety data.
| Endpoint | Rodent / preclinical | Human |
|---|---|---|
| Running endurance | Yes — increased, but in combination with exercise training | Never measured, at any dose or duration |
| VO₂ max, time trial, work capacity | Not the endpoint used | Never measured |
| Fatty-acid oxidation / fibre type | Yes — oxidative myofibre shift | Indirect: increased muscle CPT1b, more meal fat oxidised (n≈6 per arm, 2 weeks) |
| HDL cholesterol | Yes — dose-dependent rise in obese rhesus monkeys | Yes — up to +16.9% over 12 weeks (n=268) |
| Triglycerides | Yes | Yes — −16.9% (12 weeks); −30% at 10 mg (2 weeks) |
| Liver fat | Yes | −20% in a 2-week study of 6 men |
| Cardiovascular events | Not assessed | Never assessed — no outcome trial exists |
| Tumour formation | Yes — tumours after 104 weeks of dosing in rats and mice | No data whatsoever; longest human exposure is 12 weeks |
| Long-term safety | This is precisely what ended the programme | None |
The endurance claim, checked from the other side
“No human endurance trial exists” is a negative claim, so we went looking for one rather than assuming. Searching the published literature for GW-501516 against exercise capacity, VO₂ max and athletic performance returns nothing in humans. A search of ClinicalTrials.gov returns exactly three registered GW-501516 studies, all sponsored in the GSK era: two lipid trials and one study of body fat and inflammation. None has a performance endpoint. There is no registered, completed or terminated human trial of cardarine and endurance.
Two near-misses deserve to be named, because they are the closest anything has come and because neither counts:
- Mavodelpar (REN001) — a different PPARδ agonist — was tested in a randomised, double-blind, placebo-controlled Phase 2 trial of 213 patients with primary mitochondrial myopathy, with change in distance walked in a 12-minute walk test as the primary endpoint over 24 weeks. That is a genuine human exercise-capacity endpoint for the receptor class. It does not transfer to cardarine: different molecule, a rare disease population with impaired mitochondrial function rather than healthy athletes — and it did not work. Posted results show a mean improvement of 26.75 m on drug versus 30.89 m on placebo.[20] If anything, it is evidence against the extrapolation people make.
- Bocidelpar (ASP0367), another selective PPARδ modulator, reached humans in a double-blind Phase 1 study of single and multiple ascending doses in healthy adults, lasting 1 and 14 days respectively.[19] Phase 1 measures blood levels and tolerability, not performance, and again it is not cardarine.
So the honest statement is narrow and firm: every endurance claim made for cardarine rests on rodent treadmill data, and on rodent treadmill data in which the drug worked alongside training rather than instead of it.
The cancer question, stated precisely
Two independent lines of published, peer-reviewed work show PPARδ activation by GW-501516 promoting tumour growth in animals, and they are worth citing specifically rather than gesturing at:
- In Apcmin mice, which are genetically predisposed to intestinal polyposis, GW-501516 significantly increased the number and size of intestinal polyps — most strikingly a fivefold increase in polyps larger than 2 mm.[10]
- In carcinogen-initiated mice, GW-501516 drove highly metastatic squamous cell carcinomas of the forestomach within two months. The authors describe the model as one in which tumorigenesis is dependent on the PPARδ agonist.[11]
Now the counterweight, because being honest cuts both ways. The role of PPARβ/δ in carcinogenesis is genuinely contested in the field: a 2015 review in Trends in Endocrinology & Metabolismopens by noting that conflicting studies indicate PPARβ/δ both inhibits and promotes tumorigenesis, and that context-specific mechanisms may explain the contradiction.[12] Some laboratories report PPARβ/δ activation suppressing tumour growth. This is not a settled mechanism.
Three things follow, and they should be held together. First, a 104-week rodent bioassay at pharmacology-driven doses is not the same as a human dose over a human timeframe, and the standard cautions about species differences in rodent carcinogenicity apply. Second, we have no human cancer data on cardarine at all, and we never will unless someone runs a study nobody is going to run — twelve weeks is the longest anyone has ever taken it under observation. Third — and this is the part the debate does not rescue — the finding was severe enough that a sponsor walked away from a late-stage cardiometabolic asset with a genuine efficacy signal, and no company has picked it up in the two decades since. That is an unusually loud market signal about a molecule that had already cleared Phase 2 on its primary endpoint.
Regulatory status, sport, and what is actually in the bottle
Cardarine is not approved as a medicine anywhere in the world, and it never reached market. It is not a lawful dietary-supplement ingredient either. In a warning letter issued in December 2025, the FDA told a vendor that products on its site — naming “Cardarine GW501516” alongside ostarine, ibutamoren and ligandrol — are unapproved new drugs under section 505(a) of the Federal Food, Drug, and Cosmetic Act, and noted that the firm marketed the whole group under the SARM label.[13] That is the regulator documenting the same category error this page opened with.
In sport it is prohibited at all times — in and out of competition — under section S4 of the WADA Prohibited List, hormone and metabolic modulators, where PPARδ agonists are named explicitly with GW1516/GW501516 given by its full chemical name.[14] In March 2013 WADA took the unusual step of issuing a public health alert about it, warning athletes that the compound had been withdrawn from development because of serious toxicities found in preclinical studies and stating that clinical approval had not and would not be given.[15] Anti-doping bodies almost never editorialise about the health of people trying to cheat; that they did here is itself information. Detection is not an obstacle either — the sulfoxide and sulfone metabolites were characterised and built into routine doping controls back in 2010.[16] We cover the wider prohibited-substance landscape in banned peptides and WADA.
Then there is the question of what you would actually be taking. In a JAMA analysis of 44 products bought online and sold as SARMs, only 52% contained a SARM at all; another 39% contained a different unapproved drug, and GW-501516 was one of the compounds found in that undeclared group. Across the sample, no active compound at all was detected in 9% of products, substances not listed on the label were present in 25%, and the amount found matched the label in only 41%.[17] A five-year European market-surveillance study of 324 seized samples across 13 countries found cardarine among the top five molecules detected, mostly from illegal distribution, with the majority containing active — and sometimes over-stated — doses.[18] The practical translation: the label is close to meaningless, and the two failure modes run in opposite directions.
The honest bottom line
Cardarine is a well-designed molecule with a mechanism that works. PPARδ activation really does shift fuel use toward fatty-acid oxidation, and that really does show up in humans as measurable changes in muscle gene expression, meal fat handling and blood lipids.[5][6] The lipid result — HDL up, triglycerides down, apoB down, over twelve weeks in 268 patients — is the kind of Phase 2 signal that normally buys a compound a Phase 3.[6]
It did not get one. The programme ended because two-year rodent studies produced tumours, and published animal work independently shows the same agonist accelerating tumour growth in two different models.[8][10][11] Set against that: no human trial has ever tested the thing cardarine is actually bought for, the strongest rodent endurance result required training alongside the drug rather than replacing it, and the closest human exercise-capacity trial in the receptor class — a different, better-characterised PPARδ agonist — came out no better than placebo.[2][20]
So the ledger reads: an unquantified but non-trivial cancer signal, on the debit side, against a benefit that has never been demonstrated in a human being on the credit side. There is no dose that makes that trade work, which is why this page does not contain one. If the underlying goal is endurance, the interventions with actual human outcome data are unglamorous and available — structured training, and the nutritional ergogenics that have been through real trials.
This article is research information, not medical advice, and it is not a protocol. Cardarine (GW-501516) is an unapproved investigational drug whose development was discontinued after rodent carcinogenicity findings; it is not approved for human use in any country, it is not a lawful dietary-supplement ingredient, and the FDA has issued warning letters to companies selling it. It is prohibited at all times in sport, and a positive test carries the sanctions attached to a non-specified substance. Products sold online are frequently mislabelled in both directions. Nothing here should be read as a recommendation to obtain or use it; if you have taken it, tell a clinician rather than a forum.