Mounjaro vs Wegovy: Which Weight Loss Injection Is Better? A Doctor's Comparison

What Are Mounjaro and Wegovy?

Mounjaro (tirzepatide) is a weekly injection developed by Eli Lilly. It was originally approved for type 2 diabetes management and has since gained significant attention for its remarkable weight loss outcomes in clinical trials. The key feature that sets tirzepatide apart: it acts on two hormone receptors simultaneously — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1).

Wegovy (semaglutide 2.4mg) is a weekly injection developed by Novo Nordisk. It is a higher-dose formulation of the same active ingredient in Ozempic, approved specifically for chronic weight management. Semaglutide acts on GLP-1 receptors only.

Both belong to the GLP-1 class — but Mounjaro's dual-action mechanism is a meaningful clinical distinction, not just marketing language.

The Mechanism Difference: Why It Matters

GLP-1 receptor agonists work by mimicking a gut hormone that:

• Slows gastric emptying (you feel full longer)
• Reduces appetite signals in the brain
• Stimulates insulin release in response to food
• Suppresses glucagon (a hormone that raises blood sugar)

Tirzepatide adds GIP receptor activation on top of this. GIP is another incretin hormone that, when combined with GLP-1 receptor stimulation, appears to amplify both weight loss and metabolic effects. The GIP component also seems to improve tolerability at higher doses — an important clinical consideration.

Think of it this way: if semaglutide is a single-engine aircraft, tirzepatide is a twin-engine. Both fly — but the twin has more power, and the data reflects this.

The Clinical Trial Data: SURMOUNT-1 vs STEP 1

This is where the numbers speak clearly.

STEP 1 Trial (Semaglutide / Wegovy) The landmark STEP 1 trial enrolled 1,961 adults with obesity (BMI ≥30, or ≥27 with at least one weight-related complication) without diabetes. Over 68 weeks at the 2.4mg maintenance dose, participants lost an average of 14.9% of body weight — compared to 2.4% with placebo. Approximately 86% of participants lost at least 5% of body weight.

Citation: Wilding JPH et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity." N Engl J Med. 2021;384(11):989–1002.

SURMOUNT-1 Trial (Tirzepatide / Mounjaro) The SURMOUNT-1 trial enrolled 2,539 adults with obesity or overweight with at least one complication, without diabetes. Over 72 weeks, participants on tirzepatide achieved:

• 5mg dose: 15.0% average body weight loss
• 10mg dose: 19.5% average body weight loss
• 15mg dose: 20.9% average body weight loss

Placebo: 3.1% loss. 91% of participants on the 10mg dose lost at least 5% of body weight.

Citation: Jastreboff AM et al. "Tirzepatide Once Weekly for the Treatment of Obesity." N Engl J Med. 2022;387(3):205–216.

The takeaway: At its highest approved dose, tirzepatide produced approximately 6 percentage points more weight loss than semaglutide 2.4mg in separate trials. No direct head-to-head randomised trial has been published as of early 2026, so comparisons across trials must be interpreted cautiously — population differences and trial design matter. That said, the magnitude of difference is clinically meaningful and consistent across multiple studies.

Dosing Schedules

Both are weekly subcutaneous injections administered via pre-filled pen devices.

Wegovy (Semaglutide) Titration: | Week | Dose | |------|------| | 1–4 | 0.25mg | | 5–8 | 0.5mg | | 9–12 | 1.0mg | | 13–16 | 1.7mg | | 17+ | 2.4mg (maintenance) |

Mounjaro (Tirzepatide) Titration: | Week | Dose | |------|------| | 1–4 | 2.5mg | | 5–8 | 5mg | | 9–12 | 7.5mg | | 13–16 | 10mg | | 17–20 | 12.5mg | | 21+ | 15mg (maintenance) |

Tirzepatide has a longer titration schedule — up to 20 weeks to reach maintenance dose. This slower escalation helps manage side effects but means patients need patience before reaching full effect.

Side Effects: What to Expect

The most common side effects for both medications are gastrointestinal:

| Side Effect | Semaglutide (STEP 1) | Tirzepatide (SURMOUNT-1) | |------------|----------------------|--------------------------| | Nausea | ~44% | ~33% | | Diarrhoea | ~30% | ~23% | | Vomiting | ~24% | ~13% | | Constipation | ~24% | ~36% |

These are typically most pronounced during dose escalation and tend to improve over time. Eating smaller meals, avoiding fatty or rich foods, and staying hydrated can significantly reduce GI discomfort.

Both medications carry a black box warning regarding medullary thyroid carcinoma risk (based on animal studies; human relevance is unknown) and are contraindicated in patients with a personal or family history of MEN2 (multiple endocrine neoplasia type 2) or medullary thyroid carcinoma.

Neither medication is recommended during pregnancy.

Important note on muscle mass: Some studies suggest that weight loss on GLP-1 medications includes a proportion of lean muscle mass. Resistance training and adequate protein intake (1.2–1.6g per kg body weight) are strongly recommended alongside treatment.

Cost Comparison

In Singapore, both Mounjaro and Wegovy are prescription-only medications available at licensed medical clinics. Neither is currently subsidised under Medisave or standard insurance schemes for weight management indications.

Pricing varies by clinic and dose. As a general guide:

• Wegovy: Approximately SGD $300–600/month depending on dose and clinic
• Mounjaro: Approximately SGD $350–700/month depending on dose and clinic

Both represent a significant financial commitment. Medical weight management programmes that bundle medication with nutritional coaching, follow-up consultations, and body composition monitoring typically offer better long-term outcomes than medication alone.

Who Is Each Medication Better Suited For?

Consider Mounjaro (tirzepatide) if:

• You have type 2 diabetes or significant insulin resistance — the GIP mechanism provides additional glycaemic benefits
• You need to lose a larger percentage of body weight (>15%)
• You've previously tried semaglutide with limited results
• You're willing to commit to a longer titration period for potentially greater outcomes
• You tolerated Ozempic well and want to try a more potent option

Consider Wegovy (semaglutide) if:

• You've previously responded well to semaglutide (e.g., Ozempic for diabetes) and want a weight-focused dose
• You prefer the most established long-term safety profile in this class
• You want a slightly shorter titration period to reach maintenance
• Cardiovascular risk reduction is a priority — semaglutide has demonstrated CV benefit in SUSTAIN-6 and SELECT trials

Both are appropriate if:

• You have obesity (BMI ≥27.5 in Asian populations with comorbidities, or BMI ≥32.5)
• You've made genuine lifestyle modifications that haven't produced sufficient results
• You're under regular medical supervision

The Bottom Line

Mounjaro and Wegovy are both genuine medical advances in obesity treatment. The clinical trial data suggests tirzepatide produces greater average weight loss — but more isn't always better for every patient. Tolerability, individual response, existing health conditions, and cost all factor into the right choice for you.

What matters most: treatment should be medically supervised, personalised, and part of a broader lifestyle programme. These are not quick fixes — they're powerful tools that work best when combined with nutritional guidance, regular monitoring, and realistic goal-setting.

Ready to Start? Speak to a Doctor Today

Both Mounjaro and Wegovy are available through Noah and Zoey — Singapore's leading digital health platforms for men's and women's health respectively.

• Men: ofnoah.sg — consult a licensed doctor online, get a personalised weight management plan, and have medication delivered discreetly.
• Women: zoey.sg — women-focused care, licensed doctors, and weight loss programmes tailored to your goals.

No lengthy clinic visits. Start with an online consultation today.

This article is for informational purposes only and does not constitute medical advice. All weight loss medications are prescription-only and require assessment by a licensed healthcare professional. Results vary between individuals.

References: 1. Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021;384(11):989–1002. DOI: 10.1056/NEJMoa2032183 2. Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205–216. DOI: 10.1056/NEJMoa2206038 3. Ryan DH, et al. Tirzepatide versus Semaglutide in Adults with Obesity. NEJM Evidence. 2023. DOI: 10.1056/EVIDoa2300325 4. Lincoff AM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. N Engl J Med. 2023;389:2221–2232. (SELECT trial)