Creatine on Retatrutide: What the Evidence Shows

Can you take creatine on retatrutide? This is a question without a clear published answer, because retatrutide is an investigational triple hormone receptor agonist with no UK marketing authorisation, available only within authorised clinical trials. No pharmacokinetic data or official guidance on combining creatine with retatrutide has been published. This article outlines what is currently known about both substances, the side effects observed in retatrutide trials, and why anyone enrolled in a trial must consult their trial team before taking any supplement, including creatine.

What is retatrutide and what is its current status in the UK?

Retatrutide has no UK marketing authorisation and is available only within authorised clinical trials. Phase 3 trials are ongoing and no UK launch date can be given.

Retatrutide holds no marketing authorisation in the UK or anywhere else, meaning it is available only within an authorised clinical trial.^[18] It is an investigational triple hormone receptor agonist, acting on GIP, GLP-1 and glucagon receptors simultaneously.^[1][10] This triple mechanism distinguishes it pharmacologically from currently licensed treatments. No head-to-head comparisons with authorised medicines have been published to date.

Clinical research has progressed beyond Phase 2. Phase 2 findings were published in the New England Journal of Medicine.^[1] Phase 3 trials are now reporting: the TRANSCEND-T2D-1 study, examining retatrutide in people with type 2 diabetes, has released results, and data from the TRIUMPH weight-management programme have also been presented.^[2][3] These larger studies are designed to establish efficacy and safety more definitively across broader populations. Full peer-reviewed publications from all Phase 3 trials are not yet complete, so the evidence base continues to develop.

Because retatrutide is not authorised, it cannot be obtained through a pharmacy, a private clinic or an online consultation in the UK. Any product sold online under this name is not a licensed medicine and may be falsified or unsafe. If you are interested in licensed weight-management treatments, your GP is the appropriate person to discuss your options with. No UK launch date for retatrutide can be given.

Can you take creatine while on retatrutide?

There is no published guidance or interaction data on combining creatine with retatrutide; trial participants must ask their trial team before taking any supplement.

There is no official guidance, clinical trial protocol data in the public domain, or published pharmacokinetic evidence addressing whether creatine can be taken alongside retatrutide. Because retatrutide is available only within authorised clinical trials, any question about combining it with supplements, including creatine, must be directed to the trial team responsible for that individual's care. Trial protocols routinely specify which concomitant substances are permitted, and participants are expected to follow those instructions precisely.

From a pharmacological standpoint, creatine is not a drug and does not undergo hepatic metabolism via cytochrome P450 enzymes, which are the pathways most commonly implicated in drug-supplement interactions.^[6] Retatrutide, like other GLP-1 class agents, may slow gastric emptying, which can theoretically affect the absorption rate of orally ingested substances, including creatine.^[4][5] This remains theoretical in the absence of published interaction data specific to retatrutide and creatine.

It would be incorrect to state that combining the two is definitively safe or definitively harmful on current evidence. Anyone enrolled in a retatrutide trial should disclose all supplements to their trial team before taking them, and should not make changes to their supplement regimen without that team's knowledge. Self-managing this decision outside the trial framework carries risks that cannot be quantified with available data.

What does creatine actually do, and is it safe to use?

Creatine is a well-researched supplement that supports ATP regeneration during high-intensity exercise; it is generally safe in healthy adults but not recommended without supervision in kidney disease.

Creatine is one of the most extensively researched nutritional supplements available, and its general safety profile in healthy adults is well established in the scientific literature. It is a naturally occurring compound synthesised in the liver, kidneys and pancreas from the amino acids arginine, glycine and methionine, and it is also obtained through dietary sources such as red meat and fish.^[19]

In the body, creatine is stored predominantly in skeletal muscle as phosphocreatine, where it plays a central role in rapidly regenerating adenosine triphosphate (ATP) during short, high-intensity exercise.^[7][8] Supplementation increases muscle phosphocreatine stores, which can support performance in activities such as resistance training and sprinting. There is also emerging research, including systematic reviews, into creatine's potential role in preserving lean muscle mass, which is of particular interest in the context of significant weight loss, where muscle loss can occur alongside fat loss.

Creatine monohydrate is the most studied form. Common doses used in research range from 3 to 5 grams daily for maintenance, though loading protocols have also been studied.^[7][8] Side effects are generally mild and may include:

• Transient water retention in muscle tissue

• Gastrointestinal discomfort at higher doses

• A rise in serum creatinine, which can be misinterpreted on routine kidney function tests; clinicians interpreting results should be informed of creatine use

Creatine is not recommended for people with pre-existing kidney disease without medical supervision.^[9] It is not a controlled substance in the UK and is widely available as a food supplement, though food supplements are not regulated to the same standard as licensed medicines. Competitive athletes may wish to choose products that have been batch-tested for contaminants through a recognised scheme.

What side effects and risks has retatrutide shown in clinical trials?

The Phase 2 trial reported dose-dependent gastrointestinal effects, heart rate increases and injection site reactions; the full safety profile is still being established in Phase 3.

In the Phase 2 trial published in the New England Journal of Medicine, retatrutide was associated with a side effect profile broadly consistent with other GLP-1 receptor agonist class medicines, though the glucagon receptor component introduces some additional considerations.^[1] The most commonly reported adverse effects were gastrointestinal in nature, including nausea, vomiting, diarrhoea and constipation. These were generally dose-dependent and most frequent during dose escalation.

The UK SmPC for licensed GLP-1 class medicines notes that acute pancreatitis has been reported, including post-marketing reports of necrotising pancreatitis and reports with a fatal outcome. While retatrutide is not yet licensed and has no UK SmPC, participants in trials should be aware of symptoms such as persistent severe abdominal pain and should report these to their trial team immediately.

GLP-1 class medicines are also associated with gallbladder and biliary disease.^[16][17] Participants should be aware of symptoms such as persistent pain in the upper right abdomen or yellowing of the skin or eyes, and should report these to their trial team promptly.

Heart rate increases were observed in the Phase 2 data, which is a known pharmacological effect of glucagon receptor agonism.^[1][10] Injection site reactions were also reported. As with licensed GLP-1 medicines, class information advises that people with pre-existing diabetic eye disease should be monitored, as rapid improvement in blood glucose control may be associated with transient worsening in those with pre-existing pre-proliferative or proliferative diabetic retinopathy.^[13][14]

Because retatrutide is investigational, its full safety profile is not yet established. The Phase 3 programme will provide more comprehensive safety data across larger and more diverse populations. Trial participants should carry their trial card or participant information sheet and show it to any healthcare professional they see, including in an emergency, so that clinicians are aware of trial participation. Suspected adverse events in trial participants should be reported to the trial team under the study protocol. Suspected side effects of medicines taken outside a trial can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Should you talk to a doctor before combining supplements with trial drugs?

Trial participants must inform their trial team before changing any supplement; outside a trial, speak to a GP or pharmacist before combining supplements with any medicine.

Anyone enrolled in a clinical trial involving an investigational medicine such as retatrutide should always inform their trial team before starting, stopping or changing any supplement, including creatine. This is not simply a precaution but a requirement of responsible trial participation. Trial protocols are designed to control variables that could affect results or participant safety, and undisclosed supplement use can compromise both.

Participants should also carry their trial card or participant information sheet at all times and present it at any healthcare encounter, including urgent or emergency care. This ensures that clinicians treating them for any reason are aware of their trial participation and can take it into account.

More broadly, the principle of disclosing all supplements to a healthcare professional applies even outside a trial context. Many supplements interact with medicines in ways that are not immediately obvious, and healthcare professionals cannot give accurate advice without a complete picture of what a person is taking. This is particularly relevant when a medicine affects gastrointestinal motility or metabolism, as GLP-1 class agents do.

If you are not enrolled in a trial but are considering creatine alongside a licensed weight-management medicine, speak to your GP or pharmacist before starting. They can review your full medication list, consider any relevant health conditions such as kidney function, and advise accordingly. If you experience any new or worsening symptoms after starting a supplement, contact your GP. For urgent concerns, contact NHS 111 for advice, or call 999 only in a life-threatening emergency.

Finally, retatrutide trials have specific eligibility criteria. Participants who are pregnant, breastfeeding or planning a pregnancy are excluded, and appropriate contraception is required during participation. Anyone with questions about eligibility or trial participation should speak directly with a trial centre or their GP.

Scientific References

1. Triple–Hormone-Receptor Agonist Retatrutide for Obesity (Phase 2 Trial).
2. Efficacy and safety of retatrutide, a GIP, GLP-1 and glucagon receptor agonist (TRANSCEND-T2D-1).
3. Efficacy and safety of retatrutide, a GIP, GLP-1 and glucagon receptor agonist (PubMed record, TRANSCEND-T2D-1).
4. GLP-1RA-induced delays in gastrointestinal motility.
5. Drug-Drug Interactions Between Glucagon-Like Peptide 1 Receptor Agonists and Oral Medications: A Systematic Review.
6. Pharmacokinetics of the dietary supplement creatine.
7. Creatine Supplementation Beyond Athletics: Benefits of Different Types of Creatine for Women, Vegans, and Clinical Populations—A Narrative Review.
8. Creatine supplementation and endurance performance: surges and sprints to win the race.
9. Effects of creatine supplementation on renal function.
10. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial.
11. Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2 trial.
12. Contractile effects of retatrutide in isolated mouse atrial preparations.
13. NG242 Diabetic retinopathy: management and monitoring.
14. The impact of improved glycaemic control with GLP-1 receptor agonist therapy on diabetic retinopathy.
15. Addressing the risk of ocular complications of GLP-1RAs; a multi-disciplinary expert consensus.
16. Association of Glucagon-Like Peptide-1 Receptor Agonist Use and Gallbladder or Biliary Disease.
17. GLP-1 receptor agonists: reminder of the potential side effects and to be aware of the potential for misuse.
18. Medicines and Healthcare products Regulatory Agency.
19. Creatine synthesis is a major metabolic process in neonatal piglets and has important implications for amino acid metabolism and methyl balance.
20. Advances in the management of obesity: non-pharmacological strategies, herbal formulations, current pharmacotherapy, emerging drugs, and future perspectives.
21. Cardiovascular effects of incretin receptor agonists: beyond glycemic control.

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