ACP-105 and Post-Cycle Therapy: What the Evidence Actually Shows

Key takeaways

What Is ACP-105?

ACP-105 is a non-steroidal, orally bioavailable selective androgen receptor modulator (SARM) that was developed by ACADIA Pharmaceuticals. The company announced preclinical data on its "ACP-105 Selective Androgen Receptor Modulator (SARM) program" at the Experimental Biology 2008 meeting, and a full medicinal chemistry characterization by Schlienger and colleagues was published in the Journal of Medicinal Chemistry in 2009.

ACP-105 was never advanced into human clinical trials. Secondary sources describe the program as having been shelved after the 2008 presentation, and no subsequent Acadia disclosures or ClinicalTrials.gov listings show it progressing further. The compound has since resurfaced in two contexts unrelated to approved medicine: as a research chemical sold online for laboratory use only, and as an analyte of interest in anti-doping and forensic toxicology, where it continues to be detected in doping-control and contaminated-supplement testing.

Different sources list different CAS registry numbers for the molecule. Recent toxicological literature uses CAS 1048998-11-3, while most chemical-supplier listings (GlpBio, MedKoo, Cayman Chemical, Selleck, AbMole, Xcess Biosciences) use CAS 899821-23-9 for what appears to be the same structure. This inconsistency itself reflects the compound's status as an obscure, unregulated research chemical rather than a fully standardized pharmaceutical entity.

ACP-105 shares its chemical origin with a related ACADIA compound, AC-262536, another aniline-derived SARM from the same discovery program. Both are distinct from later, more commonly discussed SARMs such as ostarine (enobosarm) or LGD-4033 (ligandrol), which come from different chemical series.

Does ACP-105 Suppress Testosterone? What the Preclinical Data Actually Show

The only pharmacological data on ACP-105 come from animal studies. In the original characterization work in castrated rats, the compound was reported to produce a robust anabolic effect on the levator ani muscle, described in the source publication as a large reversal of orchiectomy-induced atrophy, while producing a substantially smaller reversal of prostate involution at the same dose, consistent with the tissue-selectivity profile that defines the SARM class. Cell-based assays reported potent, high-affinity binding to the androgen receptor.

It is important to be precise about what has and has not been directly measured for ACP-105 itself. A closely related ACADIA compound from the same discovery program, AC-262536, has separately published data showing that it reduces plasma luteinizing hormone (LH) levels in castrated rats while increasing levator ani weight. Some secondary and vendor sources describe similar LH-suppressing activity for ACP-105, but the publicly available literature reviewed here does not contain a clearly documented, directly attributable LH measurement for ACP-105 itself, as distinct from its sister compound. This distinction matters: it is not established beyond doubt that ACP-105's own characterization data include a rat LH-suppression endpoint, even though such suppression would be mechanistically expected given its behavior as an androgen receptor agonist.

Mechanistically, androgen receptor activation in the hypothalamic-pituitary axis is the same negative-feedback pathway by which exogenous testosterone and anabolic-androgenic steroids suppress endogenous testosterone production, and it is also the mechanism by which SARMs with actual human trial data, including ostarine and LGD-4033, have been shown to suppress testosterone in a dose-dependent way in people. There is no published reason to think ACP-105 would be exempt from this feedback mechanism. However, because ACP-105 has never been dosed in humans, and because the specific LH data for this molecule (as opposed to its chemical relative) is not clearly documented, the magnitude, dose-dependence, and time course of any suppression in people can only be inferred by analogy, not read directly from a confirmed data point for this exact compound.

Is There Any Human Data on ACP-105 and PCT?

No. There are no published human pharmacokinetic studies, phase 1 trials, case series, or hormonal-recovery studies of ACP-105. The literature search for this article turned up only preclinical rodent pharmacology from 2008-2009, animal (rat and equine) in vivo and in vitro metabolite-identification work conducted for anti-doping purposes, and recent in silico (computational) toxicology papers that predict properties such as absorption, blood-brain-barrier penetration, and cardiac ion-channel liability rather than measuring them in living humans.

Because ACP-105 has never been evaluated in a ClinicalTrials.gov-registered human study, there is no dataset on baseline testosterone, LH, FSH, or SHBG changes during or after use in people, no data on the time course of any recovery, and no controlled comparison of any recovery intervention against placebo. Any "PCT protocol for ACP-105" circulating on forums or vendor sites is therefore not derived from human trial data on this specific compound. At best it is an extrapolation from what has been observed with other, better-studied SARMs; at worst it is simply invented.

A comprehensive in silico ADME study of ACP-105 (using seven independent computational models) predicted extensive metabolism via cytochrome P450 enzymes, identifying six predicted metabolites formed primarily through CYP3A4, with additional contributions from CYP2C9, CYP2C19, and CYP2D6. Separately, ACP-105 and its metabolites have been characterized in rat and equine urine and tissue for anti-doping detection purposes. None of this metabolic characterization work includes hormonal or clinical outcome data in humans; it exists to support doping-control detection methods, not to describe what happens physiologically in a person who has taken the compound.

What "PCT" Means for SARMs in General, and Why It Is Extrapolated Here

Post-cycle therapy, as discussed in the bodybuilding and performance-enhancement literature, generally refers to the use of selective estrogen receptor modulators (SERMs) such as tamoxifen or clomiphene, sometimes alongside human chorionic gonadotropin (hCG), for a period after stopping an androgenic compound, with the stated goal of stimulating LH and FSH output and restoring endogenous testosterone production faster than would occur without intervention. This practice was developed for anabolic-androgenic steroid users and has since been extended by analogy to SARMs.

For SARMs with actual human trial data, the evidence for suppression itself is considerably stronger than the evidence for any recovery protocol. A systematic review of SARM safety in healthy adults identified 33 studies, comprising 15 case reports or case series and 18 clinical trials, with a total of 1,447 individuals exposed to a SARM across the clinical-trial portion of that dataset. That review, along with the underlying trial literature it draws on, documents that SARMs such as ostarine and LGD-4033 produce measurable, generally dose-related suppression of testosterone in short-term human trials, even at doses well below what is typically used recreationally.

What none of the human SARM trials summarized in that review did was test a SERM-based or hCG-based recovery protocol against placebo. The recommendation to use a SERM after a SARM cycle, widespread in online SARM guides, is derived from steroid-era PCT practice and from the plausible mechanism of LH/FSH stimulation, not from controlled trials in SARM users. For ACP-105 specifically, there is no human trial of any kind, so even this indirect analogy to other SARMs is one additional step removed from data.

Because of this evidence gap, this article describes what has been reported and practiced in the wider SARM literature and community rather than recommending any specific recovery regimen for ACP-105, since no such regimen has been tested for this compound in humans.

Legal Status, FDA Position, and Anti-Doping Status

No SARM, including ACP-105, is approved by the FDA for any human use. The FDA has repeatedly warned that body-building products containing SARMs are unapproved drugs associated with serious safety concerns, including the potential to increase the risk of heart attack or stroke and life-threatening reactions such as liver damage. The agency issued warning letters to companies distributing SARM-containing products beginning in 2017 and has continued to issue warning letters through at least December 2025, and it issued renewed public warnings in 2023 specifically about products marketed to teens and young adults. A 2023 systematic review of SARM safety states plainly that SARMs are not FDA approved and that obtaining SARMs for personal use is illegal in the United States.

Secondary sources describe ACP-105 as having been placed under the World Anti-Doping Agency's "other anabolic agents" prohibited category alongside SARMs generally since 2008, which would make its use grounds for sanction in any sport that follows the WADA Code, in or out of competition. A 2025 in silico toxicology paper on ACP-105 independently confirms that the compound is increasingly detected in anti-doping analyses, underscoring that it continues to appear in doping-control screening despite never having been an approved or marketed drug.

Because ACP-105 is sold only as a "research chemical," typically labeled "not for human use" or "for research use only" by the same vendors selling it, there is no regulatory oversight of the manufacturing, purity, or labeling of any product sold under this name. This is a quality and legal concern independent of whatever pharmacological effects the molecule itself might have.

Documented and Potential Harms

Because ACP-105 itself has no human trial record, harm data must be drawn from the broader SARM class and from computational toxicology predictions specific to ACP-105. The FDA describes SARMs as a class as being associated with increased risk of heart attack or stroke, liver injury or failure, psychosis or hallucinations, sleep disturbance, sexual dysfunction, infertility, pregnancy miscarriage, and testicular shrinkage, based on adverse event reports collected across multiple SARMs. The systematic review of SARM safety in healthy adults found 15 case reports of drug-induced liver injury across various SARMs, along with isolated reports of Achilles tendon rupture and rhabdomyolysis, and reported that elevated liver enzymes occurred in a meaningful minority of clinical-trial participants across the SARM class, though most elevations were mild and reversible.

For ACP-105 specifically, a 2025 in silico toxicology study modeled properties such as gastrointestinal absorption, plasma protein binding, blood-brain-barrier penetration, and metabolic pathways using multiple computational platforms, since real toxicological data in animals or humans remain sparse. These are computational predictions, not measured outcomes in living organisms, and different modeling platforms did not fully agree with one another; some vendor sources describing ACP-105 report minimal predicted blood-brain-barrier penetration, while the dedicated in silico toxicology paper found penetration was predicted in most of its seven models. This disagreement itself illustrates how little is firmly established about the compound's disposition in the body.

Separately, ACP-105 has been studied in mouse models of radiation-induced cognitive impairment (a model relevant to cancer-treatment side effects) and in a mouse model of Alzheimer's-disease-type amyloid pathology, based on its anabolic and central nervous system activity in rodents. These are lines of basic neuroscience research interest and have no bearing on the safety of using the compound outside a monitored laboratory setting, nor do they constitute evidence about muscle-building use in humans.

No published source has quantified how large a testosterone suppression, if any, ACP-105 produces in humans, how long recovery might take, or whether any intervention shortens that recovery. The rodent tissue-selectivity data (levator ani versus prostate reversal) is the most directly documented pharmacology that exists for this specific molecule, and even the animal-level LH-suppression evidence often cited for ACP-105 appears, on close reading of the primary literature, to belong more clearly to a related compound from the same discovery program than to ACP-105 itself.

Bottom Line: Grading the Evidence

The case that ACP-105 suppresses the hypothalamic-pituitary-testicular axis in humans rests entirely on mechanistic plausibility and analogy, not on direct measurement. The compound acts as an androgen receptor agonist, and every SARM that has been tested in human trials to date has shown measurable testosterone suppression through this same receptor-mediated feedback pathway. That is a reasonable basis for expecting some degree of suppression from ACP-105 as well.

However, the directly documented animal data for ACP-105 itself consist of tissue-selectivity findings (a strong anabolic effect on the levator ani muscle with a comparatively small androgenic effect on the prostate in castrated rats), not a clearly attributable LH-suppression measurement, computational ADME/toxicology modeling, and animal metabolite-identification work performed for doping-detection purposes. There is no human data of any kind, and therefore no evidence-based way to state how much suppression occurs, how long any recovery takes, or whether any SERM- or hCG-based recovery protocol would help, hurt, or do nothing in a person who has used this compound.

Given this, any specific PCT protocol for ACP-105 found online should be understood as an unverified extrapolation, not a tested intervention. The compound is not FDA-approved, is not a legal dietary supplement, is associated (as a class member of SARMs generally) with serious documented harms including liver injury and cardiovascular risk, and is sold exclusively as an unregulated research chemical with no quality assurance behind any specific product.

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