Retatrutide (development name LY3437943) is an experimental medicine from Eli Lilly for the treatment of obesity and type 2 diabetes. It is the first triple-receptor agonist, activating the GLP-1, GIP and glucagon receptors. In phase 2 clinical studies (TRIPHASE-1), the highest dose (12 mg) showed an average weight loss of 24% in 48 weeks — more than any other weight-loss medication has ever demonstrated.

Is retatrutide available in the Netherlands?

No. As of May 2026, retatrutide has not yet been approved by the EMA or FDA. It is in phase 3 trials (TRIUMPH programme), which are expected to be completed in 2026-2027. EMA approval is expected in 2027-2028. Regular sale in the Netherlands through pharmacies will follow after that. Providers already supplying retatrutide through 'research peptides' or the grey market are operating outside the law and do not guarantee pharmaceutical quality.

How does retatrutide differ from Mounjaro?

Mounjaro (tirzepatide) is a dual agonist: it activates GLP-1 and GIP. Retatrutide is a triple agonist: it adds the glucagon receptor. Glucagon activation increases energy expenditure and fat burning in the liver, which explains why retatrutide produces more weight loss at a comparable dose (24% vs 22%). The side-effect profile is comparable to other GLP-1s: nausea, diarrhoea and constipation during the titration phase.

Can Go Leaner prescribe retatrutide?

Not until it has EMA approval. At Go Leaner, our BIG-registered doctors prescribe only EMA-approved medication: semaglutide (Ozempic, Wegovy, Rybelsus), tirzepatide (Mounjaro), liraglutide (Saxenda) and orlistat. We advise patients interested in retatrutide to await the phase 3 trials and in the meantime start with an approved alternative; tirzepatide (Mounjaro) comes closest in terms of effectiveness.

Triple-receptor agonist · in development

Retatrutide

Q: How much does retatrutide cost?

Retatrutide does not yet have official pricing because it is not on the market. Estimates based on comparable GLP-1s and the production costs of peptides suggest a wholesale price in the same range as Mounjaro (€200-€400 per month at maximum dose). The final patient price in the Netherlands will be determined by GVS negotiations after EMA registration.

The next generation of weight-loss medication from Eli Lilly. The first medicine that activates the glucagon receptor in addition to GLP-1 and GIP — achieving up to 24% weight loss in clinical studies.

Important: as of May 2026, retatrutide has not yet been approved by the EMA or FDA and is not available from Dutch pharmacies. The information below is based on phase 2 clinical studies (TRIPHASE-1) and the ongoing phase 3 trials (TRIUMPH programme). EMA approval is expected in 2027-2028.

Active substance

Retatrutide

Mechanism

GLP-1 + GIP + glucagon

Weight loss phase 2

24% (12 mg, 48 wks)

Available NL

Expected 2027-2028

What is retatrutide?

Retatrutide (development code LY3437943) is a peptide medicine from Eli Lilly — the same manufacturer as Mounjaro and Zepbound. It is injected subcutaneously once a week and is under clinical evaluation for two indications: chronic weight management in obesity and glycaemic control in type 2 diabetes.

What sets retatrutide apart is its mechanism of action. Existing GLP-1 medications activate one (Ozempic, Wegovy, Saxenda) or two (Mounjaro) hormone receptors. Retatrutide is the first medication to activate three at once: GLP-1, GIP and glucagon. This triple-receptor activation explains the exceptionally high effectiveness seen in phase 2 research.

The TRIPHASE-1 study (published in The New England Journal of Medicine, 2023) showed that patients with obesity and no diabetes lost an average of 24.2% of their body weight in 48 weeks at the highest dose (12 mg). By comparison: tirzepatide (Mounjaro) reaches around 22% in 72 weeks, semaglutide (Wegovy) around 15% in 68 weeks.

The triple-receptor mechanism of action

Each of the three activated receptors contributes to weight loss and metabolic control in a different way:

Glucagon-like peptide-1

GLP-1

Slows gastric emptying, prolongs satiety, reduces appetite via the hypothalamus, stimulates insulin release. Known from Ozempic, Wegovy, Rybelsus and Saxenda.

Glucose-dependent insulinotropic polypeptide

GIP

Enhances satiety and insulin release. Adds a synergistic effect on weight loss. Known from Mounjaro/Zepbound.

Glucagon receptor activation

Glucagon

Raises basal metabolism and stimulates fat burning in the liver (lipolysis). This is the unique element of retatrutide and explains the additional weight loss on top of GLP-1/GIP.

It is counter-intuitive that glucagon activation helps with weight loss — glucagon actually raises blood sugar. Eli Lilly designed retatrutide so that the GLP-1 and GIP activation more than compensate for the blood-sugar-raising effect, while the thermogenic (fat-burning) effect remains.

Clinical results

Results from the TRIPHASE-1 study (NEJM, June 2023), the first large phase 2 study in adults with obesity and no diabetes (n=338, 48 weeks).

Dose	Weight loss 48 wks	% patients >15% loss	% patients >25% loss
Placebo	-2.1%	2%	0%
1 mg	-8.7%	27%	0%
4 mg	-17.1%	63%	24%
8 mg	-22.8%	83%	48%
12 mg (highest)	-24.2%	83%	48%

At the end of the study, weight loss had not yet plateaued — the curve was still heading downwards. The likely explanation is that the full effect is only reached after 60-72 weeks. The phase 3 TRIUMPH trials run longer and will confirm this.

Retatrutide versus other GLP-1 medications

How does retatrutide compare to the medication that is currently available in the Netherlands?

	Retatrutide	Mounjaro	Wegovy	Ozempic
Manufacturer	Eli Lilly	Eli Lilly	Novo Nordisk	Novo Nordisk
Receptors	GLP-1 + GIP + glucagon	GLP-1 + GIP	GLP-1	GLP-1
Active substance	Retatrutide	Tirzepatide	Semaglutide	Semaglutide
Administration	Injection once a week	Injection once a week	Injection once a week	Injection once a week
Max weight loss	~24%	~22%	~15%	~10%
Status NL (May 2026)	Not approved	Approved	Approved	Approved
EMA expectation	2027-2028	Available	Available	Available

Side effects in phase 2 studies

The side-effect profile of retatrutide is comparable to other GLP-1 medications. Gastrointestinal effects are the most prominent and occur mainly during the titration phase.

Common (>10%)

Nausea (38% at 12 mg)
Diarrhoea (27%)
Constipation (24%)
Vomiting (16%)
Slight increase in heart rate (4-7 bpm)

Points under investigation

Increased heart rate — being studied in phase 3
Risk of pancreatitis (GLP-1 class effect)
Suspected MTC with a family history
Long-term data still limited

How much does retatrutide cost? Costs, reimbursement and insurance

As of May 2026, retatrutide is not yet officially available in the Netherlands. Eli Lilly has not yet set a pharmacy price because the phase 3 TRIUMPH trials run until 2026-2027. Preliminary indications from US market analysts suggest that retatrutide could cost between €350 and €500 per month at launch — comparable to Mounjaro and Wegovy.

Reimbursement: once retatrutide is approved by the EMA for obesity, the Dutch National Health Care Institute (Zorginstituut) will assess whether it fits within the basic health insurance package. Based on the current Wegovy/Mounjaro precedent (GVS criteria: BMI ≥35, or BMI ≥30 with comorbidity, after 6 months of combined lifestyle intervention), partial reimbursement for specific patient groups is plausible.

Supplementary insurance: some supplementary policies (CZ Plus, VGZ Aanvullend Goed, ZilverenKruis Aanvullend Extra) already offer partial reimbursement for GLP-1 medication outside the basic package. For retatrutide this remains unknown until after market authorisation.

In the meantime, the Go Leaner Basic Programme costs €199/month (medication costs separate) for the most effective, EMA-approved options such as Mounjaro and Wegovy. Our BIG-registered doctor will assess whether reimbursement is possible in your situation.

Buying or ordering retatrutide in the Netherlands — is it possible yet?

Short answer: no. Retatrutide is an investigational medicine without Dutch or European market authorisation. It is legally unavailable from Dutch pharmacies, cannot be prescribed by Dutch doctors, and is not covered by insured care.

Providers already selling retatrutide via US web shops, "research peptide" shops or grey-market channels are operating outside the Dutch Medicines Act (Geneesmiddelenwet). The Dutch Health and Youth Care Inspectorate (IGJ) has explicitly warned about this. Fines and criminal prosecution are possible for the buyer, not just the supplier.

What can you do now?

Start with an EMA-approved GLP-1 that is already available — our BIG-registered doctor will assess whether Mounjaro (22% weight loss in 72 weeks) is right for you.
Book an eligibility intake to see which medication currently gives the best results.
Sign up for our newsletter — you will be notified as soon as retatrutide receives EMA approval and becomes available at Go Leaner.

Retatrutide versus Mounjaro, Wegovy and Ozempic: the figures

Comparison of clinical results, mechanism and availability of the four most powerful GLP-1 receptor medicines in 2026.

Property	Retatrutide	Mounjaro	Wegovy	Ozempic
Active substance	Retatrutide	Tirzepatide	Semaglutide 2.4 mg	Semaglutide 1 mg
Receptors	GLP-1 + GIP + Glucagon	GLP-1 + GIP	GLP-1	GLP-1
Administration	Injection once a week	Injection once a week	Injection once a week	Injection once a week
Weight loss (max dose)	24.2% in 48 wks	22.5% in 72 wks	14.9% in 68 wks	9.6% in 68 wks
EMA approval	Expected 2027+	Yes (2022)	Yes (2022)	Yes (2018)
Available via Go Leaner	Not yet	Yes, from €199/month	Yes, from €199/month	Yes, from €199/month
Best alternative?	—	Strongest EMA option	Balanced	Entry level

Source: Jastreboff et al. (TRIUMPH, NEJM 2023); Aronne et al. (SURMOUNT-1, NEJM 2022); Wilding et al. (STEP-1, NEJM 2021).

Retatrutide pen, dosing and injection protocol

In the TRIUMPH phase 2 trial, retatrutide was administered via a prefilled injection pen, comparable to the Mounjaro KwikPen. Subcutaneous injection once a week, preferably on the same day of the week at a standardised time. Injection sites: abdomen, thigh or upper arm — rotate each time to prevent lipohypertrophy.

Dosing schedule (TRIUMPH protocol):

Weeks 1-4: 1 mg/week (starting dose)
Weeks 5-8: 2 mg/week
Weeks 9-12: 4 mg/week
Week 13+: titration to 8 mg or 12 mg/week, depending on tolerance and goal

Gradual titration is crucial for minimising gastrointestinal side effects. In phase 3 (TRIUMPH-4), an even higher dose (15-16 mg) is also being tested for patients with BMI ≥40.

Important: the information above is based on Eli Lilly publications. The final dosing and injection protocol may be adjusted at EMA authorisation based on phase 3 data.

Warning: grey-market retatrutide

Because retatrutide is not yet approved but receives a great deal of publicity, providers are increasingly appearing online selling it through "research peptides" or grey-market channels. These providers operate outside the Dutch Medicines Act (Geneesmiddelenwet) and outside pharmaceutical oversight.

Risks of grey-market retatrutide: unknown concentration and purity, no sterility guarantee, incorrect dosing (overdose = serious danger), endotoxins from poor manufacturing, false identification of the molecule, no medical supervision during use.

Go Leaner's advice: wait for the phase 3 results and EMA registration. Anyone who wants maximum weight loss under medical supervision now can start with tirzepatide (Mounjaro). This is an EMA-approved dual agonist with effectiveness almost equivalent to retatrutide and is already fully available in the Netherlands.

Want to start the most effective alternative now?

Tirzepatide (Mounjaro) is currently the most effective EMA-approved weight-loss medication in the Netherlands. Our BIG-registered doctors assess whether it is right for you and monitor your treatment from A to Z.

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