You have been trying to lose weight for years. Diets only work temporarily. Exercise helps, but finding time to consistently exercise is difficult. You found online ads for compounds that claim to be exercise in a pill. The websites claim increased fat burning, improved endurance, and better metabolic health.
What are exercise mimetics?
Exercise mimetics are substances that reproduce some effects of exercise in mouse experiments, creating hope that they will be "exercise in a pill" for people, improving insulin sensitivity, increasing mitochondrial activity, increasing fatty acid metabolism, and strengthening cardiac and skeletal muscle. Exercise mimetics are designed to activate the biological pathways exercise does without requiring exercise. The underlying science is theoretically compelling but preliminary. Marketing is too far ahead of experimental results. Those who take the current iterations of exercise mimetics are, effectively, guinea pigs.
This post discusses SLU-PP-332, its successor SLU-PP-915, and MOTS-c. None of these compounds are approved for use in humans, but people can still get them.
SLU-PP-332
SLU-PP-332 activates estrogen-related receptors. The receptors are named "estrogen-related" because they structurally resemble estrogen receptors. They do not bind estrogen and are not involved in hormonal signaling. Estrogen-related receptors regulate energy metabolism, including mitochondrial function. Activating these receptors or increasing their number reversed metabolic syndrome and improved exercise capacity in thirty mice, some of whom were genetically engineered (Billon et al., (2024)).
Having an effect in mice is not the same as having an effect in humans. The effects of a compound in animals do not always translate to humans. Many compounds that appear promising in animals ultimately fail in human studies because they prove ineffective, unsafe, or both. This is something the movies leave out. Currently, there are no published clinical trials demonstrating that SLU-PP-332 improves weight loss, endurance, diabetes, cardiovascular disease, or longevity in humans.
Despite being sold by peptide vendors, it is not a peptide but a small molecule. This means it can be taken as a pill.
SLU-PP-915
SLU-PP-915 is a newer compound developed by the group that made SLU-PP-332. They modified SLU-PP-332 to be more potent and last longer. Like SLU-PP-332, SLU-PP-915 has demonstrated exercise-mimetic effects in animal models. There are currently no published studies evaluating its effect in humans. Like SLU-PP-332, it is available online, another example of moving from the laboratory to the market without adequate scientific vetting.
MOTS-c
MOTS-c is a peptide. It occurs naturally in our bodies and appears to regulate insulin sensitivity, glucose utilization, and mitochondrial function. MOTS-c levels were higher in 10 marathoners than in 12 sedentary people (Feng et al., (2025)), but this does not demonstrate that increasing MOTS-c in the sedentary people will give them the benefits of being a marathoner. There are currently no published studies demonstrating that MOTS-c improves weight loss, endurance, diabetes, cardiovascular disease, or longevity in humans.
Treating diabetic rats treated with MOTS-c decreased fasting glucose levels, improved glucose homeostasis, and decreased degree of cardiac hypertrophy. In separate experiments on cells in the same paper, treatment with MOTSAt the subcellular level, MOTS-c increased mitochondrial function, specifically oxidative phosphorylation, but also increased reactive oxygen species (ROS) levels and decreased ATP hydrolysis rate during anoxic conditions (Pham et al., (2025)).
Sourcing
You can buy these substances online. Vendors sell them for "research purposes". This market is unregulated. There is no guarantee that the product you receive contains what the label says it contains. If you chose to use one of these substance, I recommend requesting a certificate of autheticity even thought they are not equivalent to the quality-control systems used in pharmaceutical manufacturing.
Although there is some legerdemain with how the pharmaceutical industry prices its products, it is costly to reliably mass-produce a pill that contains the same amount of a substance and no impurities. Sigma-Aldrich sells 5 mg of SLU-PP-332 for $106. Gentleman Peptides sells 60 1 mg capsules for $68, 16 times cheaper. Peptide source sells 100 1mg tablets for $100, almost 20 times cheaper. If a deal appears too good to be true...
While researching for this post I noticed that some websites selling exercise mimetics included citations of effects in humans that either did not support the claims being made or were not real. I am not going to name names. It is reasonable to check the citations provided by the manufacturer to see if they are real and support the claims being made.
What side effects have you seen?
Over the last 4 months I have seen 6 patients in the Emergency Department who were suffering from intense nausea and muscle aches. All were taking SLU-PP-332, MOTS-c, and a GLP-1 agonist or retatrutide. And they were escalating doses. Unfortunately, it is not possible determine which medication caused what symptom during an ER encounter. These cases should not be interpreted as proof that SLU-PP-332 or MOTS-c caused the symptoms. They do illustrate that the public is experimenting on themselves while the formal safety data are lacking.
Can exercise mimetics replace exercise?
In theory yes. That does not mean that these three compounds are the ones that do. Eventually, a mimetic might reproduce some metabolic effects of exercise. It might not reproduce improvements balance, strength, bone density, cardiovascular conditioning, sleep, mood, or functional independence.
Anticipated toxicity
If you are concerned about adverse effects from exercise mimetics, consult a toxicologist.
When the toxicity of a new compound is unknown or not well-described by prior studies, I focus on timing, co-exposures, product identity, dose, symptoms, vital signs, and laboratory evidence of organ injury. If possible, testing the product itself can be more informative than relying on the label, because the production process for research chemicals is not standardized or regulated. In particular, I:
- look at the temporal relationship between the substance and the symptoms
- analyze leftover from the batch the person used to determine their actual composition
- obtain labwork to determine how much of the substance is in the person's system when they are symptomatic.
Bottom line
The science behind exercise mimetics is exciting. Compounds such as SLU-PP-332, SLU-PP-915, and MOTS-c provide valuable tools for understanding how exercise affects metabolism.
Whether they ultimately become useful therapies remains unclear.