SLU-PP-332

SLU-PP-332 is a small-molecule pan-agonist of the estrogen-related receptor family (ERRα, ERRβ, ERRγ) — orphan nuclear receptors that, despite the name, do not bind estrogen. They sit at the top of the transcriptional cascade that skeletal muscle uses to respond to endurance training. Activate them pharmacologically and you can reproduce a meaningful slice of the "I just ran for an hour" gene program without actually running.

ERR Binding and PGC-1α Recruitment#

SLU-PP-332 binds the ligand-binding domain of all three ERR isoforms with low-to-mid nanomolar potency (ERRα EC₅₀ ~98 nM, with weaker but still physiologically relevant activity at ERRβ and ERRγ). Binding stabilises the receptor in its active conformation and drives recruitment of PGC-1α, the master coactivator of mitochondrial biogenesis. Once PGC-1α is in the complex, the downstream transcriptional program — fatty-acid oxidation enzymes (CPT1B), oxidative phosphorylation subunits (COX4I1), Krebs-cycle machinery, and the acute-exercise marker Ddit4 — gets pulled up to or above levels seen after a treadmill bout.

"Compound 3 [SLU-PP-332] activated ERRα- and ERRγ-dependent reporter assays and induced the transcriptional program of acute exercise in mouse skeletal muscle, mimicking in vivo physical activity." — Billon C, Sitaula S, Banerjee S, et al. ACS Chem Biol, 2023

Practical translation: within 2–3 weeks on a real dose, users report the same kind of between-set recovery and steady-state capacity improvements you'd expect from a conditioning block — without having actually done the conditioning block.

Mitochondrial Biogenesis and Substrate Switching#

The downstream consequence of sustained ERR/PGC-1α activation is more mitochondria, with higher oxidative capacity per gram of muscle. Treated rodents show increased mitochondrial-DNA copy number, higher oxidative enzyme content, and — most importantly for the recomp-focused user — a shift in whole-body substrate utilisation toward fatty acids. Resting energy expenditure rises. Fat-oxidation rate at submaximal work rises. Respiratory exchange ratio drops.

This is why SLU-PP-332 behaves like a non-stimulant fat-loss tool: it doesn't suppress appetite and it doesn't hit the adrenergic system. It just raises the metabolic floor and biases fuel selection toward fat. Anyone who compensates by eating more gets nothing; anyone holding a modest deficit gets a meaningful tailwind.

Endurance Capacity Without the Training Stimulus#

The headline effect — the one that got the compound on every biohacker feed in 2023 — is the untrained-mouse endurance phenotype.

"Mice receiving the drug ran 70 percent longer and lost about 12 percent of their body weight in 28 days, with no changes in activity or food intake compared to controls." — University of Florida News, 2023

Mechanistically this is the same ERR→PGC-1α→mitochondrial-capacity axis expressing as work output rather than body composition. For physique users this matters in two places: (1) pre-show conditioning phases where cardio volume is already ruinous, and (2) GLP-1 cuts, where aggressive fat loss threatens work capacity and the ERR signal appears to blunt that drop. Pairing with cardarine (PPARδ) layers a parallel oxidative-transcription axis on top of the ERR one, which is why that stack has become the default non-stimulant endurance protocol.

Fat Mass Reduction via Peripheral Metabolism, Not Appetite#

Unlike GLP-1 agonists, SLU-PP-332 loses fat without touching appetite or satiety. In obese mice the compound dropped body weight and fat mass at a matched food intake — meaning the entire effect came from the energy-expenditure side of the equation.

"SLU-PP-332 treatment resulted in a significant decrease in body weight and fat mass in obese mice, with enhanced endurance exercise capacity and improved glucose homeostasis." — Billon C, Schoepke E, Avdagic A, et al. J Pharmacol Exp Ther, 2024

Clean mechanistic complementarity with GLP-1s: retatrutide/tirzepatide cut intake, SLU-PP-332 raises expenditure and preserves oxidative capacity. They don't step on each other.

Cardiac ERRγ Signalling — the Mechanism Behind the Caveat#

The same receptor biology that drives the upside creates the one real safety watchpoint. ERRγ is expressed heavily in cardiac tissue, and chronic ERRγ activation engages GATA4-mediated hypertrophic signalling. High-dose rodent studies have shown measurable increases in heart-to-body-weight ratio, and this is the specific mechanistic reason users running ≥300 mg/day for extended blocks should pull an echo. It is also the reason pre-existing cardiac hypertrophy or cardiomyopathy is a hard contraindication rather than a soft caution — you're directly stimulating the pathway the diseased heart is already over-running.

The other mechanistically-driven caveat is hepatic: transcriptional remodelling of fatty-acid handling in liver tissue produces dose-dependent ALT/AST elevations in rodents at higher exposures, which is why monthly LFTs are the minimum reasonable monitoring cadence at mg-scale doses.

Common (most users)#

• Transient fatigue or "flu-like" malaise in the first 5–10 days. Consistent with an acute mitochondrial-remodeling signal — your muscle tissue is being told to behave like it just ran a marathon. Push fluids, sodium, and carbs; drop the dose by 50% for a week if it doesn't fade.
• Injection-site irritation or lumps. SLU-PP-332 is water-insoluble and carried in oil or DMSO, so SC injections can sting and leave small nodules. Rotate sites (delts, ventroglutes, quads), warm the oil before drawing, and use a 27g or smaller pin.
• Transient sleep changes. Most users report slightly better sleep at 50–200 mg/day; some report lighter or fragmented sleep at higher doses. Shift the second dose earlier in the afternoon (no later than 5 pm) if sleep quality drops.
• Reduced pump / flat look on longer runs. ERR activation pushes substrate preference toward fatty acids and depletes muscle glycogen over time. Cycle 4–8 weeks on, 2–4 weeks off, and keep carbs in pre-training meals rather than cutting them for "synergy."
• Appetite unchanged. Not really a side effect, but a recurring user complaint — SLU-PP-332 raises energy expenditure, it does not suppress hunger. If you eat back the deficit, you get nothing. Pair with a deliberate food plan or with a GLP-1 if hunger is the bottleneck.

Uncommon (dose-dependent or individual)#

• ALT/AST elevations. Rodent data show ≥2× baseline ALT/AST at the ≥100 mg/kg mouse dose range, and the community has seen liver-enzyme bumps at the 400–800 mg/day human doses.

  "ALT and AST elevations were reported at SLU-PP-332 doses of ≥100 mg/kg in rodents, indicating dose-dependent hepatic stress. No clinical trials in humans have been published to date." — Eissa, UJPR 2025

  Pull a CMP at baseline and every 4 weeks. If ALT/AST cross ~2× upper-normal, drop dose by half or stop. Do not stack with oral AAS, high-dose cardarine, or other hepatically-loaded compounds without bloodwork bookends.

• Resting HR or BP drift. Anecdotal at higher doses; track both daily. A persistent 10+ bpm climb in resting HR is a reason to cut the dose.

• "Wired but tired" at high doses. Reported around 600–800 mg/day — the endurance-gene program is running at full tilt and the body feels under-recovered. Drop to the 200–300 mg/day range.

• Flat / depleted appearance for physique-focused users on long runs. Driven by the chronic glycogen-depletion signal seen in rodent muscle at 12 weeks. Cap cycles at 8–12 weeks and refeed aggressively on the back end.

Rare but serious#

• Cardiac hypertrophy. This is the single biggest unanswered safety question with SLU-PP-332. ERRγ activation can drive GATA4-mediated cardiac hypertrophy, and high-dose rodent work has shown measurable increases in heart-to-body-weight ratio. Clinical relevance at human exposures is unknown but not zero. Warning signs: unexplained shortness of breath, new exertional chest tightness, palpitations at rest, or a persistent climb in resting HR. Stop and pull an echo. If running ≥300 mg/day for more than 8 weeks, bake the echo in proactively rather than waiting for symptoms.
• Significant hepatic injury. Beyond the routine enzyme drift — jaundice, dark urine, right-upper-quadrant pain, or LFTs >3× upper-normal. Stop immediately.
• Counterfeit / mis-dosed product harm. At 100–400 mg/day, any inaccuracy in vendor labeling or concentration becomes clinically meaningful. Most real-world "SLU-PP-332 went wrong" stories trace back to unverified powder rather than the molecule itself. Insist on a batch-specific HPLC COA, or don't run the compound.

Hard contraindications#

• Pre-existing cardiac hypertrophy, cardiomyopathy, or uncontrolled hypertension. Do not run SLU-PP-332. The ERRγ/GATA4 pathway is the specific mechanism of concern and this is not a risk to negotiate with.
• Elevated baseline LFTs. Fix the underlying cause first; do not layer an ERR agonist on top of an already-stressed liver.
• Pregnancy or active conception attempts. No reproductive-tox data exist for SLU-PP-332. Non-negotiable — wait until after.
• Stacking on top of multiple hepatotoxic agents simultaneously (oral AAS + high-dose cardarine + ketoconazole + SLU-PP-332). Pick your hepatic load deliberately and monitor.

Gender and hormonal considerations#

SLU-PP-332 is non-hormonal. It is not androgenic, estrogenic, or HPG-suppressive, so no PCT is required and the compound can run through a PCT to preserve conditioning without interfering with LH/FSH recovery. Women can use the same mg/kg-scaled dosing framework as men — there is no virilization risk. The pregnancy contraindication above applies equally to anyone who is or may become pregnant; reproductive-tox data simply don't exist for this molecule and that gap is not worth bridging on yourself.