The first months of obesity treatment with semaglutide or tirzepatide

Treatment with semaglutide (Wegovy) or tirzepatide (Mounjaro) injections starts at the lowest dose. The doctor increases it gradually, no more often than every 4 weeks, to limit nausea, vomiting and diarrhoea. The maintenance dose of semaglutide, 2.4 mg, is taken from week 17 at the earliest. Tirzepatide is taken at 2.5 mg for the first 4 weeks and then at 5 mg. The doctor moves to a higher dose only if they consider it necessary (1, 2). In the first month, you are therefore on a low dose, and it is still too early to judge how well the treatment works.

In the STEP 1 trial, adults without diabetes lost an average of 14.9% of their body weight on semaglutide after 68 weeks. In the SURMOUNT-1 trial, the average weight loss after 72 weeks of tirzepatide treatment ranged from 15.0% to 20.9%, depending on the dose. Participants in both trials also received advice on eating and physical activity (3, 4). According to the guidelines of the Polish Society for the Treatment of Obesity (PTLO), the doctor assesses whether semaglutide is working after 3 months on the 2.4 mg dose (5). Earlier follow-up appointments are used to check how the patient tolerates the medicine and to decide whether to increase the dose.

In brief

• The starting dose, 0.25 mg of semaglutide or 2.5 mg of tirzepatide, is not a maintenance dose. If your weight goes down slowly in the first month, that does not mean the medicine is not working.
• The dose is not increased more often than every 4 weeks, and the doctor decides on every change. At Nasz Gabinet, the doctor decides on the dose every month based on the weight and body measurements the patient records in the app. Before increasing the dose, the doctor should know about nausea, missed doses, a planned pregnancy and any procedure under general anaesthesia.
• In the STEP 4 trial, people who reached the 2.4 mg dose of semaglutide within 20 weeks weighed on average 10.6% less than at the start of the trial. The SURMOUNT-1 analysis included 1,775 participants treated with tirzepatide for whom measurement results were available. After 8 weeks, 62% of them had lost at least 5% of their body weight.
• According to the Polish guidelines, a medicine is working if body weight has fallen by at least 5%. With semaglutide, the doctor assesses this after 3 months on the 2.4 mg dose, which is in the 7th month of treatment at the earliest. With other medicines, the timing of the assessment depends on the medicine and on how treatment is going.

How are semaglutide and tirzepatide doses increased in the first months?

Both medicines are given once a week, and treatment starts at a dose that is not yet a maintenance dose. The semaglutide dose is increased every 4 weeks up to 2.4 mg. The tirzepatide dose is increased from 2.5 to 5 mg after 4 weeks, and each further 2.5 mg increase is possible only after at least 4 weeks on the current dose, and the doctor decides on it (1, 2).

Tirzepatide doses were increased this way in the SURMOUNT trials, but not every patient needs to reach 15 mg. The maintenance doses are 5, 10 and 15 mg (2). In adults who had a BMI of at least 30 at the start of treatment, the doctor may increase the semaglutide dose to 7.2 mg after at least 4 weeks on 2.4 mg. If the higher dose does not help control body weight better, the doctor goes back to 2.4 mg (1). Semaglutide is also licensed for treating obesity as tablets taken every day, which are dosed differently from the injections.

After the first injection, the level of the medicine in the blood is not yet stable. With once-weekly dosing, semaglutide levels stabilise after 4-5 weeks and tirzepatide levels after about 4 weeks (6, 2). So during the first month, you take the lowest dose, and the amount of medicine in your body is still building up.

Does the dose of obesity medication have to be increased every 4 weeks?

Not always. The dose is increased gradually to reduce the risk of gastrointestinal symptoms. If nausea, vomiting or diarrhoea are severe, the doctor may delay increasing the semaglutide dose or go back to the previous dose until the symptoms ease (1). The tirzepatide dose is increased only when necessary, and 5 mg is already one of the maintenance doses (2). The doctor decides on every change at a follow-up appointment, after checking how your body weight is changing and how you are tolerating the medicine. You should not change the dose on your own.

How is the liraglutide (Saxenda) dose increased?

Liraglutide is given every day. Treatment starts at 0.6 mg a day, and the dose is increased by 0.6 mg no more often than once a week, up to 3.0 mg. The patient can be on this dose from week 5 at the earliest. If the patient tolerates the medicine poorly for two weeks after a dose increase, the doctor considers ending treatment. If body weight has not fallen by at least 5% after 12 weeks on the 3.0 mg dose, treatment should be stopped. In liraglutide trials, among people who had not lost 5% by that point, 93.4% had not lost 10% after a year (7).

What happens to your appetite in the first weeks on semaglutide or tirzepatide?

One of the ways semaglutide and tirzepatide work is by acting on the areas of the brain that regulate appetite. You feel less hungry and, after eating, fuller and more satisfied. Both medicines also slow stomach emptying, so food stays in the stomach longer, although this effect weakens over time (1, 2).

Semaglutide reduces the urge to snack and to eat fatty food. In a phase I trial, people who had been taking it for 20 weeks ate 35% fewer calories than people on placebo when they could eat as much as they wanted at a meal (1). Tirzepatide reduces the appetite for snacks and for sweet and fatty food. We write separately about where constant thoughts about food come from and how the medicine changes them.

Does obesity medication work if you don't have nausea?

The medicine can work even if you do not have nausea. In semaglutide trials, body weight went down regardless of whether the patient had nausea, vomiting or diarrhoea (1). In an analysis of the SURMOUNT-1 trial, nausea in the first 8 weeks was reported by 20% of people who lost weight quickly during this time and by 14% of those who lost weight more slowly. The course and severity of gastrointestinal symptoms were similar in both groups, and most participants did not report any such symptoms at all. The authors caution that these symptoms should not be used to predict the effect of treatment (8). However, you do need to tell the doctor about nausea before the dose is increased.

What should you eat when obesity medication takes away your appetite?

When your appetite is low, it is easy to eat too little, especially protein. In an analysis of body composition in STEP 1 participants, most of the weight lost was fat, but lean body mass, which includes more than just muscle, also decreased (11). How much protein to eat, how to spread out your meals and what to eat on days with nausea is covered in our article on what to eat on obesity medication.

How much weight can you lose in the first months on semaglutide or tirzepatide?

In the trials, weight started to fall in the first weeks of treatment, and the loss slowed over the following months. In the STEP 4 trial, people who reached the 2.4 mg dose of semaglutide within 20 weeks weighed on average 10.6% less than at the start. In those who continued taking 2.4 mg, body weight fell by a further 7.9% over the next 48 weeks, calculated from their weight at week 20 (9).

How much weight did STEP 1 participants lose on semaglutide?

The STEP 1 trial included 1,961 adults without diabetes who had a BMI of at least 30, or at least 27 and a condition related to excess body weight. At the start, they weighed on average about 105 kg. After 68 weeks, people treated with semaglutide weighed on average 15.3 kg less, and people on placebo 2.6 kg less. Of the participants treated with semaglutide, 86% lost at least 5% of their body weight (3).

How much weight did SURMOUNT-1 participants lose on tirzepatide?

The SURMOUNT-1 trial included 2,539 adults without diabetes who weighed on average 104.8 kg at the start. For 72 weeks, they took tirzepatide at a dose of 5, 10 or 15 mg, or placebo. The dose was increased every 4 weeks, and the dose escalation period lasted up to 20 weeks. After 72 weeks, people treated with tirzepatide weighed on average 15.0%, 19.5% or 20.9% less, depending on the dose, and people on placebo 3.1% less. Between 85% and 91% of those treated lost at least 5% of their body weight (4).

What if your weight goes down slowly in the first 8 weeks on tirzepatide?

If you lose weight slowly at first, that does not mean the treatment is not working. A later analysis of the SURMOUNT-1 trial compared the results of 1,775 participants for whom body weight measurements were available. For the first month they took tirzepatide at 2.5 mg, and for the second month at 5 mg.

After 8 weeks of treatment, 62% of participants had lost at least 5% of their body weight. In the remaining participants, the average weight loss was 3.1%. The researchers then compared the results of both groups after 72 weeks of treatment:

All weight loss was calculated relative to weight at the start of the trial (8).

The analysis was carried out after the trial had ended and was funded by the manufacturer of the medicine, so its results need to be treated with caution. The calculations included only measurements from the period when participants were taking the medicine. The averages given here should therefore not be compared with those in the main SURMOUNT-1 publication.

What affects how fast you lose weight on semaglutide or tirzepatide?

Participants in the STEP and SURMOUNT trials received advice on eating and physical activity. In SURMOUNT-1, they were advised to eat 500 kcal a day less and to do 150 minutes of physical activity a week (8). In semaglutide trials, women, people without type 2 diabetes and people with a lower starting body weight lost relatively more weight (1). Results from different trials should not be used to rank the medicines, because the trials included different people and lasted for different lengths of time. The doctor chooses the medicine, taking into account the patient's medical conditions and how the patient tolerates treatment.

For someone weighing 100 kg, a 5% loss means 5 kg. According to the Polish guidelines, for most patients the goal of the first stage of treatment is a 5-10% reduction in body weight over 3-6 months (5).

When does the doctor assess whether obesity medication is working?

According to the Polish guidelines, a medicine is considered effective if body weight has fallen by at least 5%. However, the timing of this assessment depends on the specific medicine (5). After the first month on the starting dose, it is too early to conclude that treatment is not working. The 0.25 mg dose of semaglutide is a starting dose, and the maintenance dose is 2.4 mg. The maintenance doses of tirzepatide are 5, 10 and 15 mg.

• Semaglutide: assessment after 3 months on the 2.4 mg dose, that is, after 28 weeks of treatment at the earliest, in the 7th month (5).
• Tirzepatide: there is no set point at which the medicine is stopped because of insufficient weight loss. The doctor sets the time of the assessment, taking into account the chosen maintenance dose and how treatment is going (2).
• Liraglutide: assessment after 12 weeks on the 3.0 mg dose, that is, after 16 weeks of treatment at the earliest (7).

Before deciding that a medicine is not working, the doctor checks, among other things, whether the patient is taking it as prescribed and whether anything is making it hard for them to change their eating and physical activity habits. If the control of coexisting conditions, such as high blood pressure or diabetes, has improved, the doctor may consider continuing treatment even though body weight has fallen by less than 5% (5). The rules for stopping each medicine still apply, however. Not losing weight on the starting dose is assessed differently from losing too little after some time on the therapeutic dose, or from weight loss levelling off after a year of treatment. How to tell these situations apart and what the doctor changes in each case is explained in our article on what to do when your weight stalls on obesity medication.

What do follow-up appointments look like in the first months of obesity treatment?

In the first months, the doctor decides on each dose increase at a follow-up appointment, so they need up-to-date measurements. This is how we run obesity treatment at Nasz Gabinet: the patient records their weight in the app once a week and their body measurements once a month. Every month, the doctor reviews this data and uses it to decide on the next e-prescription and dose. The programme also includes video consultations with a doctor and a psychologist. The patient buys the medicine at a pharmacy and pays for it separately, outside the programme. We refer people whose drinking is hazardous to our addiction treatment clinic alongside obesity treatment.

It is best to weigh yourself regularly, at the same time of day and on the same scales, so that you can see the change in body weight rather than its day-to-day fluctuations.

What should you tell the doctor before the dose of obesity medication is increased?

• Whether you have had severe nausea, vomiting, diarrhoea or constipation since the last dose increase. If the symptoms are severe, the doctor may delay the next increase.
• Whether you have missed any doses. After several missed doses of semaglutide, the doctor considers restarting treatment at a lower dose.
• Whether you are planning a pregnancy. Semaglutide needs to be stopped at least 2 months before a planned pregnancy, and tirzepatide at least a month before (1, 2).
• Whether you are due to have a procedure under general anaesthesia or deep sedation. The medicine slows stomach emptying, and food left in the stomach increases the risk of inhaling stomach contents (aspiration), so you also need to tell the doctor preparing you for the procedure about the medicine.
• If you are on tirzepatide: whether you take the contraceptive pill. According to the European product information, the dose of the pills does not need to be changed. The US product information recommends switching to a non-oral contraceptive method, or adding a barrier method such as a condom, for 4 weeks after starting treatment and for 4 weeks after each dose increase (2, 10). The doctor decides on the method of contraception.

Which symptoms during obesity treatment need urgent medical attention?

Severe, persistent abdominal pain, including pain that spreads to the back, means you need to contact a doctor immediately, because it may be a symptom of acute pancreatitis (1, 2). The same applies to sudden loss of vision or rapidly worsening eyesight during semaglutide treatment. If you have vomiting and diarrhoea, drink plenty of fluids, because fluid loss can put a strain on the kidneys, and contact a doctor if the symptoms persist. The most common side effects (nausea, constipation and diarrhoea) and what helps ease them are described in our article on side effects of obesity medication.

What happens after the first six months of obesity treatment with medication?

After a few months, weight loss slows down and then levels off. In the STEP 5 trial, body weight in people treated with semaglutide decreased until week 68 and then stabilised (1). The Polish guidelines advise against treatment shorter than 6 months and consider treatment lasting at least a year to be best. Some patients need the medicine long term (5).

In the STEP 1 extension, body weight rose again after semaglutide was stopped, and after a year without the medicine it was only 5.6% lower than at the start of the trial (1). When stopping makes sense and how to prepare for it is covered in our article on what happens after you stop obesity medication. This article does not replace a conversation with the doctor who is managing your treatment.

Frequently asked questions

When does semaglutide start working?

In the STEP 1 trial, body weight in people treated with semaglutide went down from the start of treatment (1). However, the first dose of 0.25 mg is not a maintenance dose, and the level of the medicine in the blood stabilises after 4-5 weeks of regular injections. According to the Polish guidelines, the doctor assesses whether semaglutide is working after 3 months on the 2.4 mg dose. At earlier follow-up appointments, the doctor checks how the patient tolerates the medicine and how their weight is changing.

How much weight can you lose in the first month on obesity medication?

There is no single result to expect after the first month of treatment. In the first month, people usually take the starting dose. An analysis of the SURMOUNT-1 trial compared body weight after 8 weeks, that is, after a month on tirzepatide 2.5 mg and a month on 5 mg. The analysis included 1,775 participants for whom measurement results were available. Of these, 62% had lost at least 5% of their body weight by then. In this group, the average loss was 7.9%, and in the others 3.1%. For a starting weight of 100 kg, this means about 8 kg and 3 kg after 8 weeks. People who initially lost weight more slowly weighed on average 14.6% less after 72 weeks.

Is Ozempic dosed the same way as Wegovy?

Ozempic and Wegovy both contain semaglutide, but Ozempic is licensed only for treating type 2 diabetes. Its dose is increased from 0.25 mg through 0.5 mg and 1 mg up to a maximum of 2 mg once a week, to improve blood sugar control (6). The semaglutide product licensed for treating obesity is Wegovy, with a maintenance dose of 2.4 mg. The doctor chooses the medicine and the dose.

What should you do if you miss a dose of semaglutide or tirzepatide?

A missed dose of semaglutide is given as soon as possible if no more than 5 days have passed since the scheduled day. If more time has passed, the dose is skipped and the next one is given on the usual day of the week (1). With tirzepatide, you have 4 days to take a missed dose (2). If several doses of semaglutide have been missed, the doctor considers restarting treatment at a lower dose, so you need to report any break before your next follow-up appointment.

Can you change the day of the week you inject semaglutide or tirzepatide?

Yes, provided at least 3 days pass between two consecutive doses. This applies to both semaglutide and tirzepatide. After that, you continue to inject the medicine once a week on the new day (1, 2).

Sources

1. European Medicines Agency. Wegovy (semaglutyd) - charakterystyka produktu leczniczego i ulotka dla pacjenta (summary of product characteristics and patient leaflet). ema.europa.eu
2. European Medicines Agency. Mounjaro (tirzepatyd) - charakterystyka produktu leczniczego i ulotka dla pacjenta (summary of product characteristics and patient leaflet). ema.europa.eu
3. Wilding JPH, Batterham RL, Calanna S et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021;384(11):989-1002. PMID 33567185, DOI
4. Jastreboff AM, Aronne LJ, Ahmad NN et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216. PMID 35658024, DOI
5. Bąk-Sosnowska M, Białkowska M, Bogdański P et al. Zalecenia kliniczne dotyczące postępowania u chorych na otyłość 2024 - stanowisko Polskiego Towarzystwa Leczenia Otyłości (Clinical guidelines for the management of patients with obesity - position statement of the Polish Society for the Treatment of Obesity). Medycyna Praktyczna, special edition, September 2024. ptlo.org.pl
6. European Medicines Agency. Ozempic (semaglutyd) - charakterystyka produktu leczniczego (summary of product characteristics). ema.europa.eu
7. European Medicines Agency. Saxenda (liraglutyd) - charakterystyka produktu leczniczego (summary of product characteristics). ema.europa.eu
8. Kokkinos A, Thethi T, Lee CJ et al. Tirzepatide Efficacy and Tolerability According to Early Weight Response: A Post Hoc Analysis of the SURMOUNT-1 and SURMOUNT-2 Trials. Diabetes Obes Metab. 2026;28(9):8367-8377. PMID 42348366, DOI
9. Rubino D, Abrahamsson N, Davies M et al. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity: The STEP 4 Randomized Clinical Trial. JAMA. 2021;325(14):1414-1425. PMID 33755728, DOI
10. U.S. Food and Drug Administration. Mounjaro (tirzepatide) injection - Prescribing Information, 05/2022. accessdata.fda.gov
11. Wilding JPH, Batterham RL, Calanna S et al. Impact of Semaglutide on Body Composition in Adults With Overweight or Obesity: Exploratory Analysis of the STEP 1 Study. J Endocr Soc. 2021;5(Suppl 1):A16-A17. PMC8089287, DOI