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Weight-Loss Injections by the Numbers: What Do Clinical Trials Say About Semaglutide and Tirzepatide?

9 August 2026·8 min read
Sources of this article were verified4 scientific references with direct, checkable links

They have become the topic of every gathering, and are sometimes sold without a prescription. Let's set out the real trial numbers — without hype and without promotion.

The numbers from the trials

In the SURMOUNT-1 trial, adults with overweight or obesity achieved weight loss of 16.0%, 21.4% and 22.5% on tirzepatide 5, 10 and 15 mg respectively[1]. In the STEP-1 trial, semaglutide achieved about 14.9%[1].

And in the head-to-head SURMOUNT-5 comparison over 72 weeks, tirzepatide outperformed semaglutide: −20.2% vs −13.7%[2],[3].

22.5%highest loss in SURMOUNT-1
(tirzepatide 15 mg)
14.9%semaglutide in
STEP-1
20.2% vs 13.7%the head-to-head
SURMOUNT-5 result

What isn't said often enough

  1. The trials weren't "injection only": trial programmes included a lifestyle intervention — the drug was added to it, not substituted for it.
  2. Muscle is part of the weight lost: which is precisely why resistance training and protein become more important, not less (the resistance article and the protein article).
  3. Stopping usually means regain: weight management is a chronic condition, and the drug is not a course of treatment that ends.
  4. They have side effects and contraindications: nausea and gastrointestinal upset are common, and some conditions rule them out entirely — a decision for a doctor, not a pharmacy or an influencer.

Our position, plainly

These are prescription medicines with real, documented results for specific groups. FitCal does not sell them, promote them, or oppose them — our role is that you know your numbers whether you are on them or not. And those using them need more dietary tracking, not less, because reduced appetite can mean inadequate protein and micronutrients.

💉 Important health and regulatory notice: Do not start or stop any medication based on an article — this information is purely educational and the decision is made with your treating physician after assessing your case. In Saudi Arabia these medicines are dispensed by prescription from a licensed practitioner and are regulated by the Saudi Food and Drug Authority; purchasing them outside licensed channels is a regulatory violation and a health risk. This article is independent educational content, not an advertisement for or endorsement of any medicine.

Scientific references

  1. GLP-1 clinical trial results database — STEP and SURMOUNT — https://www.weightlossrankings.org/research/glp1-clinical-trial-results-database
  2. Tirzepatide tops semaglutide in the SURMOUNT-5 trial (72 weeks) — https://www.appliedclinicaltrialsonline.com/view/tirzepatide-weight-loss-semaglutide-surmount-trial
  3. TCTMD coverage of the SURMOUNT-5 results — https://www.tctmd.com/news/tirzepatide-tops-semaglutide-weight-loss-surmount-5
  4. Tirzepatide after intensive lifestyle intervention: the SURMOUNT-3 trial (Nature Medicine) — https://www.nature.com/articles/s41591-023-02597-w

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Medical & legal disclaimer: Content on the FitCal blog is general education and awareness. It is not medical advice, a diagnosis, or a treatment plan, and it does not replace consulting a licensed healthcare practitioner who knows your case. Do not start or stop any medication, supplement, diet or training programme based on what you read here. Any mention of a drug, supplement or product is educational reporting of the scientific literature — not an advertisement or endorsement — and any doses cited are those used in the studies, not personal recommendations. Every figure is sourced at the bottom of each article so you can verify it yourself; if you spot an error, email us at fitcal@verokron.com and we will review and correct it. In Saudi Arabia, for health advice call 937; in an emergency call 997.