GW501516, sold as Cardarine or Endurobol, is a synthetic compound people take to get some of the effects of cardio without doing as much of it: better endurance, easier fat loss during a cut, lower triglycerides. It is popular in endurance and physique circles and usually grouped with 
SR9009 (Stenabolic) as an "exercise mimetic." It is not a steroid or a SARM, it does not touch your hormones, and it does not need post-cycle therapy.
GW501516 has real human trial data, but only for blood lipids, not for athletic performance. Every endurance and fat-loss-while-training result comes from studies in mice. And the reason it never became a drug is the bigger issue: two-year animal studies showed it caused cancer in multiple organs, which is why the manufacturer killed the program in 2007. The lipid effects in people are genuine and well documented. The endurance promise and the cancer risk are the two things to weigh.
Deep-dive
GW501516 was developed in the 1990s by GlaxoSmithKline and Ligand Pharmaceuticals as a treatment for dyslipidemia, metabolic syndrome, and cardiovascular disease. It is a potent, highly selective agonist of PPARδ (peroxisome proliferator-activated receptor delta), a nuclear receptor that acts as a transcription factor, switching sets of genes on. PPARδ is heavily expressed in skeletal muscle, where it outnumbers the other PPAR subtypes many times over, and it governs how muscle chooses and burns fuel. Activating it shifts muscle toward burning fat rather than glucose, and upregulates genes for fatty acid oxidation, mitochondrial function, and oxidative (slow-twitch, endurance-type) muscle fibres.
The endurance story is real, but it is a mouse story. The reputation comes from work in Ronald Evans' lab, where GW501516 combined with exercise reprogrammed muscle fibre composition and substantially increased running endurance in mice. A later metabolomic study in mice found GW501516 raised running endurance and the proportion of oxidative muscle fibres in both trained and untrained animals, by shifting fuel use away from carbohydrate and toward fat. Importantly, that same study found the compound and actual training did not work through identical mechanisms, so it is not simply "exercise in a capsule." The crucial caveat: there is no human trial measuring whether GW501516 improves endurance, time to exhaustion, or any athletic outcome. The fibre-switching and running data are entirely rodent.
The human data is all about lipids. GW501516 reached two phase II trials before it was abandoned, and the human evidence is genuinely solid for what it measured. In the first-in-human study, healthy volunteers given GW501516 for two weeks showed significant increases in HDL and reductions in triglycerides. A two-week trial in moderately obese men found 10 mg daily cut fasting triglycerides by about 30%, LDL by 23%, apoB by 26%, and liver fat by 20%, with reduced markers of oxidative stress and increased fat oxidation in muscle biopsies. The largest trial, 12 weeks in 268 people with low HDL, found HDL up to about 17% higher, triglycerides down about 17%, LDL down about 7%, and a shift of LDL particles from small dense toward larger, less atherogenic ones. A mechanistic study in dyslipidemic men traced these effects to faster clearance of triglyceride-rich particles and increased production of HDL components. So the lipid story is not hype. What is missing is any long-term outcome data: no trial ran long enough to show whether those number changes translate into fewer heart attacks, and the program was halted before that question could be answered.
Why it was abandoned: the cancer data. GSK ran the standard two-year carcinogenicity studies required for any drug intended for chronic use. Both the rat study and the mouse study found GW501516 caused tumours in multiple organs, including liver, bladder, stomach, skin, and others, at doses from roughly 3 mg/kg/day upward. The company discontinued all development in 2007. Two points of honest context. First, these are the dosing details people raise in GW501516's defence: the tumour doses, scaled to a human, are several times higher than the 10-20 mg most people use, and the animals were dosed daily for two years, a large fraction of their lifespan. Second, and cutting the other way, the carcinogenicity studies were only ever published as conference abstracts, not full peer-reviewed papers, so the raw data has never been openly scrutinised. "The doses were high" is a reasonable observation, but it is not the same as "it is safe at lower doses," which has never been tested in anyone.
The mechanism is the uncomfortable part. The cancer signal is not a random toxicology fluke, it is plausibly tied to how the compound works. PPARδ, the receptor GW501516 activates, is pro-angiogenic: it drives the growth of new blood vessels, partly by upregulating VEGF. That is useful for delivering fuel to working muscle, but new blood supply is also one of the things a tumour needs to grow. In ApcMin mice, which are prone to intestinal tumours, GW501516 directly promoted tumour growth via VEGF, and the authors explicitly flagged concern about PPARδ agonists in anyone at elevated colorectal cancer risk. The picture in the wider literature is genuinely mixed, some cancer cell lines are inhibited by GW501516 rather than promoted, and the effect depends heavily on tissue and model, so this is not a settled "it causes cancer" verdict. But the mechanistic concern is coherent, not hand-waving, and it has never been characterised in humans taking the compound recreationally.
Women. As with most research chemicals, there is very little to go on. The human lipid trials were conducted in men, or did not report sex-specific results, so the well-documented HDL and triglyceride effects cannot be assumed to be identical in women. The rodent endurance work was largely in male animals. PPARδ and fat metabolism interact with oestrogen signalling, and women already tend to oxidise more fat during endurance exercise at baseline, so it is plausible the response differs, but that is inference, not data. There is no validated dose for anyone, so there is no sex-specific dose. A woman considering GW501516 is in essentially the same evidence position as a man on the performance side, with the lipid data being even thinner because the trials did not represent her.
What users actually report. Anecdotal reports are more consistent for GW501516 than for many research chemicals. The common thread is improved endurance and work capacity during cardio, noticeable stamina and a higher "gear" before fatigue, often within one to two weeks, alongside easier fat loss when dieting. People generally describe it as non-stimulant: no jitter, no acute hit, just less fatigue. Reports of feeling nothing exist but are less frequent than with oral SR9009, which fits the fact that GW501516 is reasonably orally bioavailable. Worth being clear about what this is: a consistent experiential signal from the community, not a confirmed effect, since no human trial has ever measured athletic performance. Treat it as real but unverified, and weigh it against a cancer signal that is also real and also not fully characterised in humans.
Dosage:
- Typical reported range is 10 to 20 mg per day, with most people landing around 10 to 15 mg. There is no validated human performance dose, this range comes from community practice. The human lipid trials used 2.5 to 10 mg daily
- GW501516 has a long half-life, around 20 to 24 hours, so once-daily dosing holds blood levels fine. No need to split doses through the day the way SR9009 requires
- Timing is flexible. Many take it 30 to 60 minutes before training because it is psychologically tied to the workout, but with a 24-hour half-life the exact timing barely matters. Unlike SR9009 it does not act on the circadian clock, so evening dosing is not a sleep concern
- It is orally active, no need for sublingual or injectable forms. This is a genuine practical advantage over SR9009, oral GW501516 actually gets into you
- Cycles of 8 to 12 weeks are standard in community use, often with a break of similar length after. No PCT is needed, it does not suppress testosterone. The honest reason to cycle here is not receptor desensitisation, it is to limit total lifetime exposure given the cancer signal, shorter and less often is the more defensible pattern
- Often stacked with SR9009 (Stenabolic) for endurance and cutting, and sometimes with SARMs in body-recomposition stacks. Stacking unproven compounds multiplies the unknowns rather than averaging them, and adds GW501516's specific cancer concern on top of whatever the other compound carries
- Third-party testing matters. The research-chemical supply chain is unregulated, underdosed and mislabelled product is common, and GW501516 is also a known contaminant found in some supplements not labelled as containing it
- Dose-response for the lipid effects was real in trials, but more is not better given the risk profile. Stay at the low end of the range
Here's what you can expect:
If it works for you the way community reports describe, expect improved endurance and work capacity during cardio, a higher fatigue threshold, and somewhat easier fat loss in a calorie deficit, showing up over the first one to two weeks rather than immediately. It is not a stimulant, there is no acute kick, and it does not change how a single set feels the way caffeine does. It does not build muscle and it does not affect hormones.
The one effect with actual human evidence behind it is on blood lipids: lower triglycerides, lower LDL, higher HDL. If you run bloodwork before and after, this is the place you are most likely to see an objective change. Whether that lipid shift is worth the cancer signal is the real question, and it is not one the evidence can answer for you.
Side effects & risks:
- The cancer signal is the headline risk and the reason this compound is not a medicine. Two-year studies in two species found tumours in multiple organs, and the mechanism, PPARδ-driven angiogenesis and VEGF upregulation, is biologically coherent rather than a fluke. The reassuring counterpoints, high doses and long durations in the animal work, are real but do not amount to evidence of safety at lower doses, because that has never been tested. Anyone with a current or past cancer diagnosis, or strong family history, should not touch this compound
- No hormonal side effects. GW501516 does not suppress testosterone, aromatise, or affect the HPTA. This is one of the few things that can be stated with confidence and it is the main reason people pick it over steroids or SARMs
- Liver is a reasonable concern. The rat carcinogenicity study found liver tumours, the compound is metabolised by the liver, and anecdotal reports of mild liver stress exist, though the human trials, which were short, did not show significant liver enzyme elevations. Run baseline and follow-up liver panels
- Reported side effects from community use are generally mild and inconsistent: occasional headaches, lethargy, or mild GI discomfort. Because there is no trial data on recreational use, it is impossible to say how common these are
- The supply chain is a risk in itself. GW501516 sold as a research chemical is unregulated, purity varies, and it has turned up as an unlabelled contaminant in supplements. You cannot fully trust what is in the vial
- GW501516 is on the World Anti-Doping Agency prohibited list, banned at all times under the metabolic modulators category. WADA took the unusual step of issuing a public health warning about it in 2013. Metabolites are detectable in urine and hair, and it accounts for a meaningful share of anti-doping positives each year. Any tested athlete will fail
Blood markers
Lipid panel (LDL, HDL, triglycerides, apoB), baseline before starting and rechecked at the end of a cycle. This is the one place GW501516 has real human evidence, the trials consistently moved these numbers, so it is also the place you are most likely to see whether it is doing anything in you.
Liver enzymes (ALT, AST), baseline and end of cycle. The rat carcinogenicity data flagged the liver, the compound is metabolised there, and you want a reference point even though the short human trials did not show enzyme elevation.
Fasting glucose and HbA1c, baseline and end of cycle. PPARδ activation shifts fuel metabolism, and these markers tell you whether glucose handling is moving.
Full blood count and kidney function (creatinine, eGFR), baseline, as general safety markers for any unproven research chemical run for weeks at a time.
Realistically, the people who should be most rigorous about bloodwork are the ones who have already decided to use it. Run the panels, compare before and after, and let your own lipid numbers tell you whether it is working. What bloodwork cannot do is monitor the cancer concern, there is no marker that catches that early, which is the whole reason to keep exposure short and infrequent if you use it at all.
GW501516 is an unapproved research chemical, never approved for human use, sold for laboratory research only, and banned in sport by WADA.
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