Is My Weight-Loss Medication Working? How We Judge Response

The question every patient asks by month two

“I’ve been injecting for eight weeks and I’ve only lost two kilos. Is it working?”

It’s the most common question in our weight-management clinic, and the honest answer is: at eight weeks, we usually can’t tell yet — and that’s not a failure of the medication or of you. This article explains how these medications actually behave over time, what a good response looks like, and how we decide — together, with data — whether to continue, adjust, or change course.

Why the first months understate the medication

Medications like semaglutide (Wegovy) and tirzepatide (Mounjaro) are titrated: the dose is increased gradually, usually every four weeks, to let your body adjust and to keep side effects manageable. Reaching the full therapeutic dose typically takes 16 to 20 weeks — four to five months.

That means for most of your first few months, you are not yet on the dose the clinical trials tested. Judging the medication in month two is like judging a marathon at the 5-kilometre mark.

What the evidence says about “slow starters”

An older rule of thumb — still quoted online — says a weight medication should be stopped if you haven’t lost 5% of your body weight within 12 weeks. That rule was written in 2015, before the current generation of medications existed.

The newer evidence tells a different story. In a 2025 analysis of the SURMOUNT-1 trial, about one in five people on tirzepatide were “late responders” — under 5% loss at week 12. Of those late responders, around 70% went on to reach a 5% loss by week 24, and roughly 90% reached it by week 72 with continued treatment. Similar patterns have been seen with semaglutide.

In plain terms: a slow start does not predict a poor result. Most slow starters get there.

How we actually judge response at KTMC

We use a structured checkpoint rather than a rolling verdict:

1. During titration (months 1–4): the goals are tolerability and adherence, not a weight target. We track your weight and waist at each visit, manage side effects, and adjust the titration pace to you.
2. At maximal tolerated dose: once you have been on your full (or highest comfortable) dose for around four months, we make the formal assessment: have you lost at least 5% of your starting body weight?
3. If yes — you’re a responder. We continue, and discuss what a realistic further trajectory looks like for you. Many patients ultimately reach 10–15% or more.
4. If no — we act, rather than drift. In order, we check adherence and injection technique, review whether dose or agent should change (some patients respond to tirzepatide after minimal response to semaglutide, and vice versa), revisit the lifestyle foundations, and — where appropriate — discuss whether a bariatric surgical opinion would serve you better than another six months of medication.

Weight is also not the only measure. Waist circumference, blood pressure, blood sugar (HbA1c), liver enzymes and lipids frequently improve before the scale moves much — we track these at baseline, month 3 and month 6, and they count.

What this means in practice

• Don’t self-discontinue at week 8 or 10 because “nothing is happening.” The dose you’re on isn’t the dose being judged.
• Do keep the monthly reviews — dose titration is the mechanism by which the medication works, and skipped reviews are the most common reason for a flat response.
• Expect the formal verdict around months 5 to 8, depending on how quickly your titration went.
• A non-response, properly identified, is useful information — it tells us to change something, not that nothing can be done.

If you’re on a weight-loss medication — whether started with us or elsewhere — and you’re unsure whether it’s working, that is exactly the question a structured review is for.

This article describes our general approach and is not a substitute for individual medical advice. Response assessment always takes your full clinical picture into account.

References

1. Ard J, et al. Weight reduction over time in tirzepatide-treated participants by early weight loss response: post hoc analysis of SURMOUNT-1. Diabetes Obes Metab. 2025;27:5064–5071.
2. Real-world titration, persistence and weight loss of semaglutide and tirzepatide in an academic obesity clinic. Diabetes Obes Metab. 2025.
3. Real-world weight loss with semaglutide and tirzepatide in patients with overweight or obesity without type 2 diabetes (SHAPE). Adv Ther. 2025.