Peptides for Weight Loss: Complete Guide to GLP-1s & More

Why peptides for weight loss?#

The most significant advance in weight management in decades has come from peptide-based therapies — specifically GLP-1 receptor agonists like semaglutide and tirzepatide. These compounds don't simply suppress appetite through central stimulant mechanisms; they mimic endogenous gut hormones that regulate satiety, gastric emptying, and insulin secretion. The result is a fundamentally different physiological response: sustained reduction in caloric intake with improved metabolic markers. Beyond GLP-1s, a second category of peptides — including AOD 9604, CJC-1295, and Ipamorelin — work through growth hormone pathways that influence lipolysis (fat breakdown) and body composition. These are used differently, typically subcutaneously in shorter cycles, and target fat loss more directly rather than through appetite regulation. This guide covers both categories: the clinical GLP-1 receptor agonists and the research-stage growth hormone peptides, with an honest assessment of evidence strength for each.

GLP-1 receptor agonists: semaglutide, tirzepatide, retatrutide#

GLP-1 receptor agonists are the dominant peptide class for weight loss, supported by large randomised controlled trials. Semaglutide (Ozempic/Wegovy) is a GLP-1 receptor agonist with a 7-day half-life, enabling once-weekly dosing. The STEP trials showed 15–17% body weight reduction over 68 weeks in people with obesity. Compounded semaglutide is widely used as a lower-cost alternative, though it lacks FDA approval for the injectable form. Tirzepatide (Mounjaro/Zepbound) is a dual GLP-1/GIP receptor agonist. The SURMOUNT trials showed 20–22% body weight reduction — meaningfully superior to semaglutide. The GIP component appears to improve tolerability and may enhance the weight loss effect. Dosing escalates from 2.5mg weekly to a maintenance dose of 5–15mg. Retatrutide is a triple agonist (GLP-1/GIP/glucagon). Phase 2 data showed up to 24% weight reduction at 48 weeks — the highest reduction seen in a peptide trial to date. It is currently in Phase 3 trials and not yet approved. Investigational compounded versions are circulating, though evidence on long-term safety is limited. All three compounds are administered subcutaneously once weekly. Side effects are primarily GI: nausea, vomiting, and diarrhoea, especially during dose escalation.

Semaglutide, tirzepatide, and retatrutide are prescription medications or investigational compounds. Use under medical supervision.

AOD 9604: the fragment peptide#

AOD 9604 is a synthetic fragment of human growth hormone (hGH) — specifically the C-terminal amino acids 176–191. The theory is that this fragment retains the lipolytic (fat-burning) activity of hGH without the growth-promoting or insulin-sensitising effects of full-length hGH. Animal studies showed AOD 9604 increased fat oxidation and reduced adipose tissue in obese mice. However, human clinical trials for obesity were discontinued after Phase 2b, as the compound failed to demonstrate significant weight loss versus placebo at doses studied. The trials used oral formulations; some proponents argue subcutaneous injection may behave differently, but this has not been rigorously tested in humans. AOD 9604 is not FDA approved for any indication. It is sold as a research chemical. Current evidence for meaningful weight loss in humans is weak.

CJC-1295 and Ipamorelin for body composition#

CJC-1295 is a GHRH analogue — it stimulates the pituitary to release growth hormone. Ipamorelin is a GHRP (growth hormone-releasing peptide) that works via a different receptor (ghrelin receptor) to also stimulate GH release. They are commonly stacked because they work synergistically: together they produce a larger GH pulse than either alone. CJC-1295 without DAC has a half-life of ~30 minutes, requiring injection immediately before sleep (when GH is naturally elevated). CJC-1295 with DAC extends this to ~6–8 days, allowing weekly dosing. Ipamorelin has a half-life of ~2 hours. Elevated GH levels support fat oxidation, lean muscle preservation, and recovery — particularly during caloric restriction. However, the weight loss effect is indirect and modest compared to GLP-1 receptor agonists. CJC/Ipamorelin stacks are generally used by people focused on body recomposition (reducing fat while maintaining or gaining muscle) rather than pure weight loss. Typical protocol: CJC-1295 (without DAC) 100mcg + Ipamorelin 200–300mcg, injected subcutaneously 30–60 minutes before sleep, 5 days on / 2 days off. Cycle length 8–12 weeks.

Comparing the options: which peptide for which goal?#

The right choice depends heavily on your goal, access, and context. For significant weight loss (10%+ body weight): GLP-1 receptor agonists are the only peptides with robust clinical evidence. Tirzepatide shows the best efficacy data currently available. Semaglutide is widely accessible through compounding pharmacies. For body recomposition (lean gains + fat reduction): CJC-1295 + Ipamorelin stacks are commonly used, often alongside resistance training. Effects are more modest and gradual than GLP-1s, but the mechanism is different — these work by optimising GH/IGF-1 axis rather than reducing caloric intake. For injury recovery while cutting: BPC-157 and TB-500 are added to protocols primarily for tissue repair and recovery, not fat loss. However, faster recovery allows more training volume, which indirectly supports body composition goals. AOD 9604 has insufficient human evidence for a confident recommendation. It remains a popular research compound but the clinical trial programme was discontinued.

Track your protocol and progress in Staqk — set target doses, log injections, and monitor body weight trends over your cycle.

Protocol considerations and safety#

Peptides for weight loss range from FDA-approved medications to unregulated research chemicals. Key considerations: Dose escalation: GLP-1 receptor agonists require gradual dose escalation to minimise GI side effects. Never start at maintenance dose. Standard semaglutide escalation: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg (Wegovy schedule, 4 weeks per step). Composition monitoring: Weight loss on GLP-1s can include lean muscle mass loss, particularly without resistance training and adequate protein intake. Aim for 1.6–2.2g protein per kg bodyweight during a GLP-1 protocol. Cycle breaks: Research chemicals like CJC-1295/Ipamorelin are typically cycled (8–12 weeks on, 4–8 weeks off) to prevent receptor desensitisation. Not for everyone: Peptide-based weight loss therapies are contraindicated in personal or family history of medullary thyroid carcinoma or MEN2 syndrome (for GLP-1 agonists). Discuss medical history with a prescribing physician before starting.