In April 2025, the American College of Physicians released updated clinical practice guidelines for the pharmacologic treatment of obesity, recommending GLP-1 receptor agonists and other incretin-based therapies as first-line options for adults with a body-mass index of 30 or higher, or 27 with comorbidities. The guidance marks a significant shift in how mainstream medicine views weight-loss pharmacotherapy, yet it also underscores a gap that peptide researchers have been tracking for years: the risk of losing skeletal muscle alongside adipose tissue. Discussion of any compound's effects refers to outcomes observed in clinical or preclinical studies, not anecdotal reports.
The ACP guidelines cite randomised controlled trials showing that semaglutide and tirzepatide produce mean weight reductions of 10 to 15 percent over 52 to 68 weeks, with tirzepatide reaching as high as 20.9 percent in some cohorts (PubMed). What the guidelines acknowledge less explicitly is that roughly 25 to 40 percent of the weight lost on GLP-1 agonists comes from lean body mass, not fat alone (PubMed). For older adults, individuals with sarcopenia, or anyone prioritising functional strength, that proportion raises a clinical question: can a compound selectively mobilise fat while preserving muscle?
AOD-9604, a synthetic peptide fragment derived from the C-terminal region of human growth hormone (amino acids 176 to 191), was originally investigated as a lipolytic agent that lacks the insulin-resistance and hyperglycaemic effects of full-length hGH (PubMed). Preclinical rodent studies in the early 2000s demonstrated dose-dependent reductions in body fat without corresponding increases in blood glucose or IGF-1, suggesting a mechanism confined to adipocyte lipolysis rather than systemic growth signalling. A small Phase II trial in obese adults reported modest fat loss over 12 weeks, though the compound did not advance through later-stage regulatory approval for obesity (PubMed). Despite that commercial outcome, AOD-9604 remains available as a research peptide, and recent interest has centred on whether it might complement incretin therapies by offsetting muscle catabolism.
The mechanistic rationale rests on two observations. First, AOD-9604 appears to stimulate hormone-sensitive lipase and inhibit lipoprotein lipase in adipocytes, promoting triglyceride breakdown without activating the growth-hormone receptor (PubMed). Second, because it does not bind the GH receptor on muscle or cartilage, it theoretically spares the anabolic pathways that preserve lean mass. In contrast, GLP-1 agonists reduce caloric intake so effectively that energy deficit alone can drive muscle protein breakdown, especially when dietary protein and resistance training are suboptimal (PubMed). No head-to-head trial has yet compared AOD-9604 plus semaglutide against semaglutide alone with body-composition endpoints, so the hypothesis remains exactly that: a hypothesis grounded in mechanism rather than direct clinical evidence.
Who stands to be most affected by the ACP's new recommendations? The guidelines apply to roughly 42 percent of U.S. adults who meet the BMI threshold for obesity, a population that includes middle-aged and older individuals at elevated risk for sarcopenia. The document emphasises shared decision-making and notes that medication should accompany lifestyle modification, yet it does not prescribe specific resistance-training protocols or protein targets. For researchers and clinicians tracking body composition, this omission is conspicuous. A 2023 secondary analysis of the STEP-1 trial found that participants losing more than 15 percent of body weight on semaglutide also lost an average of 3.4 kilograms of lean mass, even when counselled on diet and exercise (PubMed). That figure may seem modest in percentage terms, but for an older adult with baseline sarcopenia, a 3-kilogram deficit can translate into measurable declines in gait speed, grip strength, and fall risk.
Peptide users who have been following strategies to preserve lean mass during semaglutide therapy will recognise AOD-9604 as one candidate in a broader toolkit that also includes MOTS-c, tesamorelin, and structured resistance training. MOTS-c, a mitochondrial-derived peptide, has shown promise in rodent models for improving insulin sensitivity and exercise capacity, though human data remain preliminary (PubMed). Tesamorelin, a growth-hormone-releasing hormone analogue approved for HIV-associated lipodystrophy, reduces visceral adipose tissue without the same degree of hyperglycaemia seen with exogenous GH, but it does carry a risk of elevated IGF-1 and requires daily subcutaneous injection (PubMed). Retatrutide, a triple agonist at GLP-1, GIP, and glucagon receptors, produced up to 24 percent weight loss in a 48-week Phase II study, yet body-composition data from that trial are not yet fully published (PubMed). Each compound occupies a different point on the efficacy-safety-specificity triangle, and none has been studied in combination with AOD-9604 under controlled conditions.
What does the evidence quality look like for AOD-9604 specifically? On a three-point scale, it sits at a 2: mechanistic plausibility is strong, early-phase human data exist, but no large randomised trial has confirmed clinically meaningful fat loss or muscle preservation in the context of caloric restriction. The original Phase II study enrolled 300 participants and reported statistically significant reductions in body fat by dual-energy X-ray absorptiometry, yet the absolute difference was approximately 1.5 kilograms over 12 weeks, and dropout rates were high (PubMed). More recent investigations have been limited to animal models or in-vitro adipocyte assays. That gap matters because the ACP guidelines rest on trials with thousands of participants and cardiovascular outcomes data; AOD-9604 has no equivalent evidence base. Outcomes described in studies cited here cannot be assumed to generalise to individual users.
The practical implication is that anyone considering AOD-9604 in a research or off-label setting must weigh incomplete efficacy data against the known performance of GLP-1 agonists. Semaglutide and tirzepatide have demonstrated not only weight loss but also reductions in major adverse cardiovascular events, improvements in glycaemic control, and favourable safety profiles across tens of thousands of patient-years (PubMed). AOD-9604 has no cardiovascular outcomes trial, no long-term safety registry, and no regulatory approval for any indication. It is available through research-chemical suppliers, but purity, dosing consistency, and sterility vary widely. The ACP guidelines do not address research peptides at all, which means clinicians following the new recommendations will default to FDA-approved agents unless a patient explicitly raises the topic.
What should researchers and informed consumers watch next? First, whether any investigator launches a combination trial pairing a GLP-1 agonist with AOD-9604 and body-composition endpoints measured by DEXA or MRI. Such a study would need to control for protein intake and resistance training, ideally in a factorial design that isolates the peptide's contribution. Second, whether the ongoing wave of triple- and quadruple-agonist development (retatrutide, survodutide, and others) incorporates lean-mass preservation as a co-primary endpoint rather than a secondary analysis. Third, whether real-world registry data from semaglutide and tirzepatide users reveal subgroups, older adults, those with baseline sarcopenia, or individuals losing weight rapidly, who experience disproportionate muscle loss and might benefit from adjunctive strategies.
The ACP guidelines represent a milestone in obesity medicine, but they also highlight what remains unknown. GLP-1 agonists are extraordinarily effective at reducing body weight and metabolic risk, yet the collateral loss of lean mass is not trivial. AOD-9604 offers a mechanistic rationale for selective fat mobilisation, but the clinical evidence supporting that rationale is thin. Until a well-powered trial bridges the gap, the peptide remains a research compound with theoretical appeal rather than proven utility. This is an editorial discussion of published research; it is not a treatment plan. For now, the question is not whether AOD-9604 works as well as semaglutide, it almost certainly does not, but whether it might work alongside incretin therapy to preserve the muscle that weight loss too often takes away. That question is worth asking, even if the answer is not yet in hand.