Short answer: With weight-loss injections, appetite may change in the first few days after the first injection. Weight loss is gradual: the starting dose is for tolerability, not for weight loss, so look at your weight trend over several weeks rather than single weigh-ins.

Key takeaways

  • Appetite may change in the first few days after the first injection.
  • The starting dose is for tolerability, not for weight loss, so the scales may not move much in the first weeks.
  • Weight loss is gradual; the trend over weeks matters more than any single weigh-in.
  • Haftra's Goal Weight Forecast calculates the weekly trend from at least 4 weeks of entries and shows a target date when there is enough data.

Two separate questions tend to get mixed up: when the medicine starts to work, and when you see a change on the scales. The first is usually felt in the first few days; the second is a curve that takes weeks and may not be noticeable on the starting dose.

This page is for general information only and does not promise any personal result. Responses vary from person to person; only your GP or prescriber can assess how your treatment is going.

What do you feel in the first few days?

These medicines slow stomach emptying and prolong the feeling of fullness. Pharmacologically, this effect starts after the first injection; you may notice in the first few days that you feel full sooner and your portions get smaller.

The same mechanism is also the source of side effects: nausea, bloating and constipation are most prominent in the first days and after each dose increase.

When does weight change?

The starting dose is usually not a treatment dose; its purpose is to get the body used to the medicine. That is why there may be no clear movement on the scales in the first weeks. As the dose steps go up, the effect becomes more noticeable.

The weight curve does not go down in a straight line. Day-to-day fluctuations are linked to fluid, salt, sleep and bowel movements, and are easily mistaken for the effect of the medicine. The only meaningful indicator is the trend over several weeks, not the difference between two weigh-ins.

What if it feels like it is not working?

This is a common impression in the early weeks and is often linked to the dose step. Only your GP or prescriber decides what to do (wait on the current step, increase the dose or review the treatment). Increasing the dose on your own increases side effects; it does not speed things up.

Having dated records with you when you go to a review appointment makes this assessment easier: how long you stayed on each step, how your weight changed, which side effect happened on which day.

Seeing the trend

Haftra applies a trend to your weight entries and shows the direction rather than the daily fluctuation. If there is not enough data or no clear decrease, it does not show an estimated date. It does not substitute the average from clinical trials for your own result. It is free and can be used without creating an account.

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Frequently asked questions

When do weight-loss injections start working?

The effect that slows stomach emptying and prolongs the feeling of fullness starts after the first injection; appetite may change in the first few days, and you may notice that you feel full sooner and your portions get smaller. Weight loss itself is gradual.

When does weight start to change?

The starting dose is usually not a treatment dose, so there may be no clear movement on the scales in the first weeks. As the dose steps go up, the effect becomes more noticeable.

If I do not lose weight in the first week, does that mean the medicine is not working?

No. The starting dose is for building tolerance, and how people respond varies. This is a common impression in the early weeks and is often linked to the dose step. Only your GP or prescriber decides what to do; increasing the dose on your own increases side effects and does not speed things up.

Should I weigh myself every day?

Day-to-day fluctuations are linked to fluid, salt, sleep and bowel movements, and are easily mistaken for the effect of the medicine. The only meaningful indicator is the trend over several weeks, not the difference between two weigh-ins.

How much weight loss per week is healthy on average?

The rate differs from person to person and slows over time; weight loss is gradual. What pace suits you is for your prescriber to judge.

When does weight loss stall (plateau)?

Weight loss usually slows down over time and can level off. What to do then, such as staying on the current dose, changing the dose or reviewing your eating, is for your GP or prescriber to decide.

Sources

  • EMA: Mounjaro (tirzepatide)
  • EMA: Ozempic (semaglutide)
  • EMA: Wegovy (semaglutide)
  • NHS: Obesity treatment
  • MHRA (Medicines and Healthcare products Regulatory Agency)

Last reviewed: 4 August 2026