Tirzepatide activates two incretin receptors instead of one — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 — which is why it's sometimes called a "twincretin." It's approved by prescription for type 2 diabetes, weight management and obstructive sleep apnea, and it's also sold, unregulated, as a research peptide in the same online market as semaglutide.

How it works

Like semaglutide, tirzepatide activates the GLP-1 receptor — glucose-dependent insulin release, slowed gastric emptying, increased satiety. But it also activates the GIP receptor, which plays its own role in insulin secretion and appears to work synergistically with the GLP-1 pathway on fat tissue and metabolism. That dual mechanism is the basis for tirzepatide's approvals and is the main mechanistic difference from semaglutide's single-receptor action.

Approval history

May 2022: approved as Mounjaro for glycemic control in type 2 diabetes.
November 8, 2023: approved as Zepbound for chronic weight management in adults with obesity, or overweight with a weight-related condition.
December 20, 2024: Zepbound's approval extended to moderate-to-severe obstructive sleep apnea in adults with obesity — the first medication approved specifically for OSA.

Source: FDA-approved prescribing information for Zepbound (tirzepatide) injection (opens in new tab), accessdata.fda.gov (label 217806, original approval 2023).

What the clinical trials showed

In SURMOUNT-1, the pivotal trial supporting the weight-management approval, adults with obesity (or overweight plus a weight-related condition) who didn't have diabetes lost significantly more body weight on tirzepatide than on placebo alongside diet and exercise. At 72 weeks, mean weight change was −15.0% on the 5mg dose, −19.5% on 10mg, and −20.9% on the highest, 15mg dose, versus −3.1% on placebo. These are trial averages under medical supervision, not a guarantee for any individual, and not something to extrapolate to an unsupervised, unregulated product.

Source: Jastreboff AM, et al., "Tirzepatide Once Weekly for the Treatment of Obesity," (opens in new tab) The New England Journal of Medicine, 2022.

What's different from semaglutide, practically

Both compounds are once-weekly injectables approved for overlapping indications (type 2 diabetes, chronic weight management), and both carry similar gastrointestinal side-effect profiles and the same class-wide boxed warning about thyroid C-cell tumors seen in rodent studies. The dual GIP/GLP-1 mechanism is the reason tirzepatide's own trial reported greater average weight loss than semaglutide's — but exact outcomes vary by dose, trial and individual, and neither drug's trial results translate to an unsupervised, unprescribed product.

Side effects

Per the FDA label, the most common side effects in trials (each reported by more than 5% of participants) were gastrointestinal: nausea, diarrhea, vomiting, constipation, abdominal pain, and indigestion, alongside injection-site reactions, fatigue, hair loss (alopecia), and belching. As with semaglutide, these were more frequent while the dose was still being increased.

Tirzepatide carries the same class-wide boxed warning about thyroid C-cell tumors observed in rodent studies, and the same contraindication for anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. Other label warnings include acute pancreatitis, gallbladder problems, acute kidney injury (usually linked to dehydration from GI side effects), hypersensitivity reactions, worsening diabetic retinopathy in people who already have it, and hypoglycemia when combined with insulin or a sulfonylurea — the same risk factors a prescriber is meant to screen for before a first dose.

Cost in South Africa

Prices for unregulated "research-grade" tirzepatide vary by dose and vendor. Among the vendors we've verified: Peptide Labs South Africa lists 15mg at R1,350, and Noventra Pharma lists a 30mg pre-filled pen at R2,050 (dropping to R1,850 each at 3+, per its retail-tier bulk pricing). These aren't pharmacy prices for the prescription version (Mounjaro or Zepbound) — they're what unregulated online sellers charge for a vial or pen marketed as a research chemical, with none of the pharmacy dispensing or prescriber screening that comes with the registered medicine. See our vendor comparison for how we score these sellers on documentation and transparency.

South Africa status: the same regulatory gap applies here as with semaglutide. South Africa's medicines regulator, SAHPRA, requires registration for any product intended to treat or alter a bodily function, and has publicly warned against unregistered peptide products sold online and through informal channels. A pharmacy-dispensed, prescribed medicine is not the same product — legally or in terms of what's actually verified about its contents — as an unregulated vial marketed as "research-grade tirzepatide." See how we rate for the fuller regulatory picture.

Frequently asked questions

Is tirzepatide legal in South Africa?

The prescription medicine (Mounjaro/Zepbound) requires SAHPRA registration and a valid prescription. The "research-grade" vials and pens sold online as tirzepatide are not SAHPRA-registered medicines, and SAHPRA has publicly warned against unregistered peptide products sold this way — buying them for personal use sits in a legal grey area, not a clearly regulated one. This isn't legal advice.

How is tirzepatide different from semaglutide?

Tirzepatide activates both the GIP and GLP-1 receptors, where semaglutide activates GLP-1 alone — see How it works above. That dual mechanism is why tirzepatide is often discussed as the more potent of the two in head-to-head trial comparisons, though both share a very similar side-effect profile.

How much does tirzepatide cost in South Africa?

Among vendors we've verified selling it as a research chemical, published prices range from roughly R1,350 to R2,050 depending on dose, format and vendor — see Cost in South Africa above. Pharmacy-dispensed Mounjaro/Zepbound follows a different pricing and distribution model entirely.

What are the most common side effects?

Gastrointestinal ones — nausea, diarrhea, vomiting and constipation — reported by more than 5% of trial participants, per the FDA label. See Side effects above for the full list, including the boxed warning and other risks a prescriber screens for.

Related guides

This page is educational information about a molecule and its regulatory history. It is not medical advice, not a recommendation to use tirzepatide outside a prescription, and not an endorsement of any vendor.