Mounjaro starts at a dose too low to do much for your weight. People are often surprised by that, but it is deliberate. The first four weeks are there so your stomach can get used to the medicine, and the dose that does the work comes later. So do most of the side effects.
This page goes in the order things happen: the dose steps, the side effects and when they ease, how long before you can judge the result, and what the trials found when people stopped. If you have not decided on a medicine yet, our comparison of Mounjaro and Ozempic is the better place to start. Mounjaro is the brand name for tirzepatide. It is prescription-only, and whether it suits you is a doctor's decision after an assessment.
Before the first injection
You see a doctor first. They go through your medical history, the medicines you take and your measurements, and check for anything that rules tirzepatide out, such as a personal or family history of medullary thyroid cancer or MEN2. They also ask about things that need extra care, such as past pancreatitis, or a pregnancy now or planned. The full list, and how our programme runs, is on the Mounjaro weight management programme page.
What dose does Mounjaro start at?
2.5 mg once a week for four weeks, then 5 mg. Any further increase is 2.5 mg at a time, with at least four weeks at each dose. The schedule is from the official prescribing information in the United States and Europe, and it is the fastest you can go, not a timetable everyone has to follow.
| Stage | Weekly dose | What it is for |
|---|---|---|
| Weeks 1 to 4 | 2.5 mg | A starting dose so the body can adjust. It is not a maintenance dose. |
| From week 5 | 5 mg | The first dose that can be used long term. |
| Only if needed | 7.5, 10, 12.5 then 15 mg | Each step is 2.5 mg, held for at least four weeks before the next. |
| Maintenance | 5, 10 or 15 mg | 15 mg is the maximum. |
Some people never need to go past 5 mg. If it is working and you tolerate it, there may be no reason to. Who stays there and who goes higher differs too much from person to person to predict at the start, so it is decided at your reviews rather than planned in advance. At our clinic the weekly dose is given as a shot in clinic, and your first review is about four weeks in, before any increase is discussed. The dose only goes up after a review.
When do side effects start, and how long do they last?
Mostly in the first few months, while the dose is going up, and often in the days after an injection. In the SURMOUNT-1 trial (New England Journal of Medicine, 2022), which followed 2,539 adults with obesity or overweight, it took 20 weeks to reach the top dose. The stomach side effects were mostly mild to moderate and happened mainly during that stepping-up period.
On 2.5 mg, many people feel full sooner and think about food less. At our clinic, loss of appetite is what patients mention most in the first two weeks, and some already see their weight come down or find their clothes a little looser. Others notice very little. That does not mean it is failing, since the starting dose is there to let your body adjust, not to cause weight loss. Mild nausea, a change in bowel habit or indigestion are common in these weeks.
What helps most is how you eat. Smaller plates of rice, eating slowly, stopping at the first sign of fullness, and going easy on fried food such as short eats and oily curries. Drink water through the day, more in hot weather, because vomiting or diarrhoea can dehydrate you quickly.
If side effects still bother you, tell us rather than waiting for the next review. The doctor can prescribe medicine to ease them and adjust your diet plan alongside it.
Most people carry on. In SURMOUNT-1, side effects led 4.3 percent of people on 5 mg to stop treatment, 7.1 percent on 10 mg and 6.2 percent on 15 mg, against 2.6 percent on placebo. According to the US prescribing information, most who stopped did so in the first few months, mainly because of stomach symptoms. That is why each increase waits until the last one has settled.
How common is each side effect?
These figures are from the US prescribing information, which pools the two placebo-controlled weight trials of tirzepatide. Each is the share of people who reported the effect at any point.
| Side effect | Placebo | Tirzepatide 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|
| Nausea | 8% | 25% | 29% | 28% |
| Diarrhoea | 8% | 19% | 21% | 23% |
| Constipation | 5% | 17% | 14% | 11% |
| Vomiting | 2% | 8% | 11% | 13% |
| Indigestion | 4% | 9% | 9% | 10% |
| Injection site reactions | 2% | 6% | 8% | 8% |
| Hair loss | 1% | 5% | 4% | 5% |
Nausea is the most common, reported by about one person in four on tirzepatide. Put the other way, three in four did not report it.
Does Mounjaro cause hair loss?
It can. In the two placebo-controlled weight trials, 4 to 5 percent of people on tirzepatide reported hair loss, against 1 percent on placebo. Hair shedding is also common after any fast weight loss, so if you notice more than usual, mention it at your review.
When to contact your doctor
- Severe or persistent stomach pain, especially if it spreads to the back, with or without vomiting. This can be pancreatitis and needs urgent attention.
- Pain in the upper right abdomen, fever or yellowing of the skin or eyes. Gallbladder problems are more likely as weight falls: in the pooled weight trials, gallbladder inflammation was reported in 0.7 percent of people on tirzepatide against 0.2 percent on placebo.
- Vomiting or diarrhoea that stops you keeping fluids down. Dehydration can affect the kidneys, so drink enough and seek help early.
- Low mood or unusual changes in mood. The US prescribing information advises monitoring for depression and stopping treatment if suicidal thoughts appear.
- A planned operation, endoscopy or sedation. Tell the team you are on tirzepatide, because it slows stomach emptying and that matters for anaesthesia.
- Planning a pregnancy. The European product information advises stopping tirzepatide at least one month before a planned pregnancy, because it stays in the body for some time.
How long does Mounjaro take to work?
Appetite often changes in the first weeks. Weight loss is judged over months. You spend the first month on a dose not meant for weight loss, and in the SURMOUNT-1 trial it took 20 weeks to reach the highest dose. The trial's main results were measured at 72 weeks.
By then, alongside a reduced-calorie diet and more activity, average weight loss was 15.0 percent on 5 mg, 19.5 percent on 10 mg and 20.9 percent on 15 mg, against 3.1 percent on placebo. Between 85 and 91 percent of people on tirzepatide lost at least 5 percent of their body weight, compared with 35 percent on placebo.
Those are trial averages, and nobody can tell you in advance where you will land. Weigh yourself once a week, on the same day at the same time, and bring the numbers to your review. Daily weighing mostly shows changes in water.
What if you miss a dose?
Take it if you are within four days (96 hours) of your usual day. If more than four days have passed, skip it and take the next one on your normal day. Never take two doses to catch up.
To move your injection day for good, keep at least three days (72 hours) between the two doses. Since we give the shot in clinic, tell us as early as you can and we will rearrange it.
What happens if you stop Mounjaro?
In the trials, most people regained much of the weight. The SURMOUNT-4 trial (JAMA, 2024) put 783 adults on tirzepatide for 36 weeks. The 670 who completed that period had lost 20.9 percent of their body weight on average. Half then carried on and half were switched to placebo without being told. Over the next year, those who carried on lost a further 5.5 percent, while the weight of those on placebo rose by 14 percent on average. By the end, 89.5 percent of those who carried on had kept at least 80 percent of their loss, against 16.6 percent of those who stopped.
So plan the end before the start. Ask your doctor how long you are likely to be on treatment and what happens when it finishes, and use the months on treatment to change how you eat, move and sleep. Those habits are what you keep when the injections stop.
Is there a Mounjaro tablet in Sri Lanka?
No. Tirzepatide is only made as a once-weekly injection under the skin, in Sri Lanka and everywhere else. Anything sold as a Mounjaro or tirzepatide tablet is not the licensed medicine, and you should not take it.
Semaglutide, the medicine in Ozempic, does come as a tablet. That is a different medicine with a different dose schedule, not a tablet form of Mounjaro.
Next step
If you are thinking about starting, the Mounjaro programme page sets out how treatment runs at our Colombo clinic, including the review schedule and how the cost is worked out. If tirzepatide turns out not to suit you, semaglutide weight management is the other option a doctor may discuss.
Tirzepatide is a prescription-only medicine. Nothing on this page is medical advice, a recommendation to use a particular medicine, or an offer to supply one. Whether it is suitable for you can only be decided by a doctor at an individual consultation.
Sources
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). New England Journal of Medicine, 2022; 387: 205 to 216.
- Aronne LJ et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: the SURMOUNT-4 randomized clinical trial. JAMA, 2024.
- US Food and Drug Administration. Zepbound (tirzepatide) prescribing information, 2025.
- European Medicines Agency. Mounjaro (tirzepatide) summary of product characteristics.
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