MariTide (AMG 133): Amgen's Once-Monthly Weight Loss Injection That Could Change Everything for South Africa

What if you only needed one injection per month instead of four? And what if, when you stopped the drug, the weight stayed off far longer than it does with Ozempic or Wegovy? That is the promise of MariTide (AMG 133), Amgen's next-generation weight loss injection currently in Phase 3 trials.

MariTide takes a fundamentally different approach to weight loss medication. While every other GLP-1 drug on the market or in development activates the GIP receptor, MariTide blocks it. This contrarian mechanism, combined with a once-monthly dosing schedule and evidence of sustained weight loss even after stopping treatment, makes it one of the most closely watched drugs in the obesity pipeline.

Here is what South Africans need to know about MariTide -- how it works, what the trial data shows, when it might arrive here, and how it stacks up against the medications already available at Dis-Chem and Clicks.

What Is MariTide and How Does It Work?

MariTide (development name AMG 133) is a bispecific antibody-peptide conjugate developed by Amgen. That technical term means it is a large antibody molecule with GLP-1 peptides chemically attached to it. The antibody portion targets and blocks GIP receptors, while the attached peptides activate GLP-1 receptors.

This gives MariTide two simultaneous actions:

• GLP-1 receptor agonism -- the same appetite-suppressing, insulin-sensitising mechanism used by semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro). Slows gastric emptying, reduces hunger signals in the hypothalamus, and improves blood sugar control.
• GIP receptor antagonism -- this is where MariTide diverges from everything else. Mounjaro activates GIP receptors (dual agonist). MariTide blocks them. GIP (glucose-dependent insulinotropic polypeptide) plays a complex role in fat storage. By blocking GIP signalling, MariTide may reduce fat accumulation through a pathway that GLP-1-only drugs do not touch.

Why the Antibody Structure Matters

Most weight loss drugs (semaglutide, tirzepatide, survodutide) are small peptide molecules that get cleared from your body within days. MariTide's antibody backbone gives it a half-life of approximately 3-4 weeks, which is why it only needs to be injected once per month. This long half-life also means the drug leaves your system very slowly when you stop -- potentially explaining why weight regain is delayed compared to weekly injectables.

MariTide Phase 2 Trial Results

Amgen presented Phase 2 data at the 2024 Obesity Week conference, and the results generated significant attention:

The most striking finding was the sustained weight loss after stopping treatment. With Ozempic and Wegovy, patients typically regain two-thirds of lost weight within a year of stopping. MariTide participants continued losing weight or maintained their losses for up to 150 days after their last injection. This is a potential game-changer for the weight regain problem that plagues current GLP-1 medications.

To put 14.5% in 12 weeks in context: the STEP 1 trial for Wegovy achieved 14.9% over 68 weeks, and the SURMOUNT-1 trial for Mounjaro achieved 22.5% over 72 weeks. MariTide achieved comparable percentage weight loss in a fraction of the time, though longer Phase 3 trials will show whether losses continue to accumulate.

MariTide vs Ozempic vs Mounjaro vs Wegovy

How does MariTide compare to the weight loss medications South Africans are already using or considering?

*MariTide Phase 2 data reflects only 12 weeks of treatment. Longer Phase 3 data expected 2027. Weight loss may increase substantially with longer treatment.

The Weight Regain Advantage

The biggest problem with current GLP-1 medications is what happens when you stop. Our weight regain after stopping Ozempic article details how most patients regain the majority of lost weight within 12 months of discontinuation.

MariTide's antibody structure may solve this problem in two ways:

1. Slow clearance: The antibody's long half-life (3-4 weeks) means drug levels decline gradually over months after your last injection, rather than dropping sharply within days as with semaglutide.
2. Metabolic resetting: The extended exposure period may allow the body's weight set point to adjust more thoroughly, though this hypothesis needs confirmation in longer trials.

In the Phase 2 data, participants continued to lose weight during the 150-day treatment-free period. This is unprecedented for any weight loss medication and, if confirmed in Phase 3, would fundamentally change how doctors think about treatment duration. Instead of lifelong weekly injections, patients might take MariTide for a defined course (say 6-12 months) and then stop with confidence that the weight stays off.

Side Effects and Safety Profile

MariTide's Phase 2 trial reported side effects broadly consistent with the GLP-1 drug class:

• Nausea -- the most common side effect, typically mild to moderate and improving over time
• Vomiting -- reported less frequently than nausea
• Diarrhoea -- occasional gastrointestinal upset
• Injection site reactions -- minor reactions at the injection site, expected with any subcutaneous injection
• Decreased appetite -- expected and arguably the intended therapeutic effect

Because MariTide is dosed monthly rather than weekly, patients experience the dose-escalation phase differently. The longer interval between doses may allow the body more time to adjust, though detailed tolerability comparisons with weekly drugs await Phase 3 results. For a comprehensive look at GLP-1 side effects, see our semaglutide side effects guide.

The MARITIME Phase 3 Programme

Amgen launched its Phase 3 clinical trial programme, called MARITIME, in 2024. This includes multiple large-scale trials:

• MARITIME 1 -- evaluating MariTide for chronic weight management in adults with obesity
• MARITIME 2 -- studying MariTide in adults with obesity and type 2 diabetes
• MARITIME 3 -- assessing cardiovascular outcomes in patients with overweight/obesity

Phase 3 trials typically involve thousands of participants and run for 12-18 months of active treatment. Results from the first MARITIME studies are expected around 2027, which would support a regulatory submission to the FDA. If approved in the US, Amgen would then likely pursue SAHPRA registration for South Africa.

When Will MariTide Be Available in South Africa?

Realistic timeline for South African availability:

Before SAHPRA approval, South African doctors may be able to access MariTide through the Section 21 unregistered medicines programme -- the same route currently used for Mounjaro. This requires your prescribing doctor to apply to SAHPRA on a named-patient basis, and costs are typically higher than for registered medicines.

For patients interested in medical aid coverage, it is worth noting that Discovery Health, Bonitas, and Momentum have been cautiously expanding coverage for GLP-1 medications. By the time MariTide arrives in SA, medical aid schemes may have clearer policies for obesity pharmacotherapy. The once-monthly dosing could work in MariTide's favour for medical aid approvals, as fewer injections mean lower administration costs.

What to Do While Waiting for MariTide

MariTide is still years away from South African pharmacies. In the meantime, effective options are available right now:

• Wegovy -- SAHPRA-approved, available at Dis-Chem and Clicks, R5,000-R7,000/month. The current gold standard for weight management with semaglutide 2.4mg.
• Ozempic -- SAHPRA-approved for diabetes (used off-label for weight loss), R4,500-R6,000/month. More accessible and slightly cheaper than Wegovy.
• Mounjaro -- available via Section 21, highest efficacy of any currently available drug (~22.5% weight loss). Requires doctor application to SAHPRA.
• High-protein diet -- the foundation of any weight management programme, with or without medication. Biltong, eggs, chicken, and legumes are affordable SA protein sources.
• Intermittent fasting -- free, evidence-based, and can be combined with any medication.
• Exercise -- critical for preserving lean muscle mass during weight loss, which is particularly important with GLP-1 medications.

The Next-Generation Weight Loss Pipeline

MariTide is one of several next-generation drugs that could reshape obesity treatment in South Africa over the next 3-5 years. Here is how it fits into the broader pipeline:

For the full picture, read our comprehensive next-generation GLP-1 weight loss drugs guide.

Key Takeaways

• MariTide (AMG 133) is Amgen's once-monthly weight loss injection combining GLP-1 activation with GIP receptor blocking
• Phase 2 trials showed ~14.5% weight loss in just 12 weeks, with weight loss continuing even after stopping treatment
• The sustained weight loss after discontinuation is unprecedented and could solve the weight regain problem
• Only 12 injections per year vs 52 for Ozempic, Wegovy, and Mounjaro
• Phase 3 (MARITIME) trials are underway; South African availability is estimated around 2029-2030
• Current options (Wegovy, Ozempic, Mounjaro) are available now for South Africans who do not want to wait
• Always consult your doctor before starting any weight loss medication

Last updated: June 2026. This article will be updated as new MariTide trial data becomes available. Sources: Amgen corporate presentations, Obesity Week 2024 abstracts, ClinicalTrials.gov MARITIME programme listings.