AOD 9604 with retatrutide is a combination increasingly discussed in weight-loss and body-composition circles, yet neither compound holds a Marketing Authorisation from the MHRA or EMA for use in the UK. AOD 9604 is a synthetic peptide fragment derived from human growth hormone, while retatrutide is an investigational triple incretin receptor agonist currently in Phase 3 trials. Understanding the distinct evidence base, regulatory status, and safety profile of each agent — and the complete absence of clinical data on their combined use — is essential for patients and healthcare professionals navigating this rapidly evolving and largely unregulated landscape.

What Are AOD 9604 and Retatrutide?

AOD 9604 is an unlicensed synthetic hGH peptide fragment with limited human trial data, while retatrutide is an investigational triple incretin receptor agonist; neither holds a Marketing Authorisation in the UK or EU.

AOD 9604 is a synthetic peptide fragment derived from the C-terminus of human growth hormone (hGH), specifically amino acids 176–191. Early small-scale research suggested it may stimulate lipolysis (the breakdown of fat) and inhibit lipogenesis (fat storage), with preliminary data indicating it may not significantly affect blood glucose or insulin-like growth factor-1 (IGF-1) levels. However, these findings come from limited, early-phase human studies and should not be taken as established clinical evidence. Despite initial pharmaceutical interest, AOD 9604 did not progress through the full clinical trial pathway required for regulatory approval, and it holds no Marketing Authorisation (MA) from the MHRA or EMA. It should not be used outside of regulated clinical trial settings.

Retatrutide is a more recently developed investigational compound — a triple agonist targeting the glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon receptors simultaneously. This triple-receptor mechanism is designed to produce significant reductions in body weight and improvements in metabolic parameters. A Phase 2 study published in the New England Journal of Medicine in 2023 (Jastreboff et al.) reported substantial weight loss in participants with obesity. However, retatrutide has not received approval from the MHRA or the EMA and remains an investigational agent undergoing Phase 3 trials.

Neither compound holds a valid Marketing Authorisation in the UK or EU. It is important for patients and practitioners to understand that 'investigational' or 'research' status does not equate to safety, efficacy, or regulatory approval for human use outside of controlled clinical trial settings.

Current Evidence and Regulatory Status in the UK

Neither AOD 9604 nor retatrutide is licensed by the MHRA; AOD 9604 failed to achieve regulatory approval after early trials, and retatrutide remains in Phase 3 development without NICE or MHRA guidance.

The evidence base for AOD 9604 in humans is limited. Clinical trials conducted in the early 2000s showed modest results, and the compound failed to demonstrate sufficient efficacy to support regulatory approval as a weight-loss medicine. In 2014, the US Food and Drug Administration (FDA) acknowledged a GRAS (Generally Recognised as Safe) notification for AOD 9604 as a food ingredient — meaning the FDA raised no questions about the notifier's own safety conclusion. This is not equivalent to the FDA granting approval as a therapeutic drug, and it carries no standing under UK or EU medicines law. The MHRA has not licensed AOD 9604 as a medicinal product in the UK, and its status can be confirmed via the MHRA's product licence search.

Retatrutide's evidence base is more substantial but still in development. Phase 2 trial data (Jastreboff et al., NEJM 2023) demonstrated average weight reductions of approximately 17–24% over 48 weeks — notably higher than currently approved GLP-1 receptor agonists such as semaglutide, though direct comparisons are limited by differences in trial populations and designs. Phase 3 trials are ongoing, and without completed large-scale safety and efficacy data, the compound cannot be considered ready for routine clinical use. Neither NICE nor the MHRA has issued guidance recommending retatrutide, as it remains unlicensed.

In the UK, any medicine must hold a valid Marketing Authorisation granted by the MHRA before it can be legally sold or supplied for medicinal purposes. Compounds circulating online or through private clinics without this authorisation fall outside the regulatory framework designed to protect patient safety. Patients should be aware that purchasing either of these peptides from unregulated online sources carries significant legal and health risks. To verify whether an online pharmacy is legitimate, patients should consult the General Pharmaceutical Council (GPhC) online register of pharmacies and look for the MHRA's distance-selling logo on any website selling medicines.

Potential Interactions and Combined Use Considerations

No interaction data or clinical guidance exists for combining AOD 9604 and retatrutide; combined use is speculative and may compound adverse metabolic and gastrointestinal effects with no safety framework to guide dosing.

There is no official clinical guidance, published interaction data, or regulatory framework governing the combined use of AOD 9604 and retatrutide. Because neither compound is licensed in the UK, no formal pharmacokinetic or pharmacodynamic interaction studies have been conducted or reviewed by the MHRA. Any claims about synergistic fat-loss effects from combining these agents are not supported by peer-reviewed clinical evidence.

From a theoretical pharmacological standpoint, combining a peptide with putative lipolytic activity (AOD 9604) with a potent triple incretin receptor agonist (retatrutide) could potentially amplify metabolic effects — but this is speculative and raises the possibility of compounding adverse effects with no safety data to guide dosing or monitoring. Retatrutide's glucagon receptor agonism already stimulates lipolysis and increases energy expenditure; adding AOD 9604 introduces unpredictable variables.

It is also important to note that products sold as AOD 9604 are often presented as injectable preparations, though some are marketed in oral or topical forms with unknown absorption and unverified quality. This uncertainty further complicates any assessment of combined use.

Key considerations if a patient discloses combined use include:

• Gastrointestinal effects: Both agents may independently cause nausea, vomiting, or appetite suppression; combined use could intensify these symptoms, though this is theoretical in the absence of clinical data.

• Metabolic disturbances: Excessive lipolysis may theoretically elevate free fatty acids, potentially affecting liver function or lipid profiles, though this has not been studied in this context.

• Concomitant medicines: Clinicians should review all concurrent medications, particularly insulin or sulfonylureas, given the potential for hypoglycaemia with incretin-based agents. Pregnancy and breastfeeding status should also be assessed.

• Injection site reactions: Where injectable formulations are used, there is an increased risk of localised reactions, particularly if products are sourced from unsterile or unregulated suppliers.

• Unknown long-term effects: There is no long-term safety data for either compound used individually in the general population, let alone in combination.

Healthcare professionals should approach disclosures of combined peptide use with a non-judgemental but clinically thorough assessment, and provide harm-minimisation advice where appropriate.

Safety Risks and Side Effects to Be Aware Of

Retatrutide's Phase 2 data identified nausea, vomiting, raised resting heart rate, and gallbladder events; AOD 9604's full side-effect profile is poorly characterised, and unregulated online products carry additional risks of contamination and infection.

Because AOD 9604 has not completed the full clinical development pathway, its comprehensive side-effect profile in humans is not well characterised and should not be assumed to be benign. Early trials reported it to be generally well tolerated at low doses, but these studies were small and of short duration. Reported adverse effects included mild injection site reactions and transient headaches. Products sold online as 'AOD 9604' are frequently of unknown purity, concentration, and sterility — meaning the risks extend well beyond those observed in controlled research settings.

Retatrutide's Phase 2 trial data (Jastreboff et al., NEJM 2023) identified a side-effect profile broadly consistent with other incretin-based therapies:

• Gastrointestinal: Nausea, vomiting, diarrhoea, and constipation were the most commonly reported adverse effects, particularly during dose escalation.

• Heart rate: Modest increases in resting heart rate were observed in Phase 2 trials. Increases in resting heart rate are a recognised class effect of incretin-based therapies and have been reported with GLP-1 receptor agonists more broadly, as reflected in the Summary of Product Characteristics (SmPC) for licensed agents such as semaglutide (Wegovy®) and liraglutide (Saxenda®).

• Gallbladder events: As with other incretin-based therapies, there is a potential risk of gallbladder disease, including cholelithiasis (gallstones). Patients should seek medical attention for persistent right upper quadrant or epigastric pain, fever, or jaundice.

• Injection site reactions: Localised redness, swelling, or discomfort at the injection site.

• Potential pancreatitis risk: As with other GLP-1-based therapies, there is a theoretical concern regarding pancreatitis, though causality has not been firmly established in trials to date.

For individuals sourcing either compound from unregulated online vendors, additional risks include contamination with unknown substances, incorrect dosing due to inaccurate labelling, and the use of non-sterile injection equipment, which can lead to serious infections including abscess formation or sepsis.

Patients and healthcare professionals should report any suspected side effects, adverse reactions, or defective or falsified products to the MHRA via the Yellow Card scheme (available at yellowcard.mhra.gov.uk). Patients experiencing severe abdominal pain, persistent vomiting, signs of infection, or allergic reactions should seek urgent medical attention.

MHRA Guidance on Unlicensed Peptides and Weight Loss Agents

The MHRA states it is illegal under the Human Medicines Regulations 2012 to sell or supply unlicensed medicinal products in the UK; consumers should verify pharmacies via the GPhC register and report illegal sales to the MHRA.

The MHRA has issued clear guidance on the risks associated with unlicensed medicines and research chemicals being marketed for weight loss or body composition purposes. Under the Human Medicines Regulations 2012, it is illegal to sell or supply a medicinal product in the UK without a valid Marketing Authorisation. Peptides such as AOD 9604 and retatrutide, when sold with implied therapeutic claims (e.g., fat loss, metabolic enhancement), may legally constitute unlicensed medicinal products, regardless of how they are labelled by suppliers.

It is worth noting that unlicensed medicines can be lawfully supplied in limited circumstances — for example, as 'specials' manufactured to meet the specific clinical needs of an individual patient under a prescriber's direction. This is distinct from the illegal marketing and sale of unregulated peptides online, which falls outside any legitimate supply framework.

The MHRA has previously taken enforcement action against suppliers of unlicensed injectable peptides and has issued public warnings about the dangers of purchasing such products online. The agency advises consumers to:

• Only use medicines that have been prescribed by a registered healthcare professional and dispensed by a regulated pharmacy.

• Verify pharmacies using the General Pharmaceutical Council (GPhC) online register before purchasing any medicine. For online sellers of medicines, look for the MHRA's distance-selling logo, which links to the MHRA's register of legitimate UK online medicine retailers.

• Report suspected side effects or defective/falsified products to the MHRA via the Yellow Card scheme (yellowcard.mhra.gov.uk).

• Report illegal sales or websites selling unlicensed medicines via the MHRA's dedicated enforcement reporting portal (gov.uk/report-problem-medicine-medical-device).

The legal and health risks of obtaining these compounds through grey-market channels are therefore considerable. NICE does not currently have guidance on either AOD 9604 or retatrutide, reflecting their unlicensed and investigational status within the UK healthcare system.

Speaking to a Healthcare Professional Before Use

Patients should consult a GP, pharmacist, or obesity specialist before using any unlicensed peptide; licensed UK options include orlistat, semaglutide (Wegovy®, TA875), and liraglutide (Saxenda®, TA664), all with established safety profiles.

If you are considering using AOD 9604, retatrutide, or any combination of unlicensed peptides for weight management or body composition purposes, it is strongly advisable to speak with a qualified healthcare professional before doing so. A GP, pharmacist, or specialist in obesity medicine can provide evidence-based guidance on licensed treatment options that have been rigorously evaluated for safety and efficacy within the UK regulatory framework.

Currently licensed weight management options in the UK include orlistat (available on prescription and over the counter; see NHS guidance and Xenical/Alli SmPCs), and injectable GLP-1 receptor agonists such as semaglutide (Wegovy®) and liraglutide (Saxenda®). Both semaglutide and liraglutide are MHRA-approved and are supported by NICE technology appraisals — TA875 for semaglutide and TA664 for liraglutide — which set out specific eligibility criteria. Eligibility is assessed on an individual basis by a clinician in line with NICE guidance; these treatments are not universally available to all patients. These medicines have well-characterised safety profiles and are prescribed within a structured clinical pathway that includes monitoring and follow-up. Where appropriate, referral to a specialist Tier 3 weight-management service may also be considered.

You should contact your GP, call NHS 111, or seek urgent medical advice if you are currently using unlicensed peptides and experience any of the following:

• Severe or persistent nausea, vomiting, or abdominal pain

• Signs of infection at an injection site (redness, swelling, warmth, discharge)

• Unexplained changes in heart rate or palpitations

• Symptoms of an allergic reaction (rash, swelling, difficulty breathing)

• Persistent right upper quadrant pain, fever, or jaundice (which may indicate gallbladder problems)

• Significant unintentional weight loss or fatigue

Call 999 or go to your nearest emergency department if symptoms are severe or rapidly worsening.

Healthcare professionals who encounter patients using unlicensed peptides should approach the conversation without judgement, document use carefully, and consider appropriate baseline investigations including liver function tests, lipid profile, and renal function. Concomitant medicines — particularly insulin or sulfonylureas — should be reviewed for interaction risk, and pregnancy or breastfeeding status should be assessed. Suspected side effects or falsified products should be reported via the MHRA Yellow Card scheme. Open dialogue is essential to ensuring patient safety in an environment where access to unregulated compounds is increasingly common.

Frequently Asked Questions