Appetite may begin to change within the first days or weeks of treatment with Mounjaro, Wegovy or Ozempic. Some patients start to see weight changes from around week two, while others take longer to respond. Where needed, your endocrinologist will increase the dose in steps, which takes around four to five months for Mounjaro and the Wegovy injection. In clinical trials, average weight loss was measured over 68 to 72 weeks.
- Semaglutide, the active ingredient in Wegovy, peaks in the blood one to three days after an injection, as its prescribing information states.
- The prescribing information for tirzepatide gives a median time to maximum concentration of 24 hours, with steady levels after four weeks of weekly doses.
- Some of the early change on the scale can be body water, released as the body uses its glycogen stores.
- The prescribing information schedules gradual dose increases to lower the risk of nausea and other digestive side effects.
- Average weight loss was around 15% over 68 weeks in the STEP 1 trial of the Wegovy injection and around 20% over 72 weeks in the SURMOUNT-1 trial of Mounjaro.
- Among the GLP-1 tablets, Foundayo reaches its peak level within hours of a dose and steady levels after around a week.
- The prescribing information sets a standard schedule of dose increases, and your endocrinologist will agree each step with you at the monthly follow-up.
How quickly do weight loss injections start working?
A weight loss injection is absorbed over the first few days after a dose. The Wegovy prescribing information states that semaglutide reaches its maximum concentration in the blood one to three days after a dose. The prescribing information for tirzepatide in weight management gives a median time of 24 hours for tirzepatide, the active ingredient in Mounjaro. These peak levels describe how the medication is absorbed, and they do not show when appetite or weight will change.
The half-life of semaglutide is around one week, and that of tirzepatide around five to six days. These long half-lives allow a single injection once a week. With weekly doses, tirzepatide reaches steady levels in the blood after around four weeks.
Appetite may begin to change within the first days or weeks, although the response differs from one patient to another. Our article on what GLP-1 is explains how these medications act on appetite.
What to expect in the first four weeks
Early changes on the scale can partly reflect changes in body water, rather than fat loss alone. Your body stores carbohydrates as glycogen, which is stored together with water. When glycogen stores decrease, some of that water is lost too.
Losing 2 kg in the first week does not mean you have lost 2 kg of body fat. Some patients start to see changes within the first couple of weeks, while others take longer. Starting weight is an important factor. Someone starting at 110 kg may lose more weight over the same period than someone starting at 72 kg, as energy requirements and the relative size of the calorie deficit differ.
Treatment starts at a low dose for at least four weeks. Side effects such as nausea or constipation can be particularly pronounced in the first few days at a new dose. They often improve as your body adjusts, although some symptoms last longer. If you experience nausea or constipation, your endocrinologist can adjust the pace of dose increases and, where needed, prescribe medication to help manage these side effects.
At Endocare, our endocrinologists typically observe weight loss of three to four kilos a month in patients on a medically supervised programme. Our article on how many kilos you can lose in a month explains what a realistic monthly rate looks like.
Months two to five: why the dose is increased in steps
After at least four weeks on a dose, your endocrinologist can increase it to the next step. The prescribing information for each injection gives the purpose of the gradual dose increase as reducing the risk of digestive side effects.
For the Wegovy injection, the schedule in the prescribing information reaches the 2.4 mg dose from week 17 at the earliest. In SURMOUNT-1, a 72-week clinical trial of tirzepatide in adults with obesity or overweight, the dose increases took up to 20 weeks.
The prescribing information for each medication sets a standard schedule of dose increases. Your endocrinologist will agree each increase with you at your monthly follow-up and may slow the pace if side effects are difficult to tolerate. The first doses of each medication are steps in the dose escalation, not maintenance doses. The prescribing information sets the doses for continued treatment, and your maintenance dose is not necessarily the highest one.
How weight loss builds over time in clinical trials
In STEP 1, a Phase 3 clinical trial in adults with obesity or overweight, patients taking the Wegovy injection at 2.4 mg lost an average of around 15% of their total body weight over 68 weeks. In SURMOUNT-1, a Phase 3 clinical trial in adults with obesity or overweight, patients taking tirzepatide, the active ingredient in Mounjaro, at the highest dose lost an average of around 20% of their total body weight over 72 weeks.
In OASIS 4, a Phase 3 clinical trial in adults with obesity or overweight, patients taking the Wegovy pill lost an average of around 17% of their total body weight over 64 weeks. In ATTAIN-1, a large Phase 3 clinical trial in adults with obesity or overweight, participants taking the highest dose of orforglipron lost around 12% of their body weight on average, with some achieving 15% or more. That trial lasted 72 weeks.
These figures describe the result after more than a year of treatment. They cannot be read as a rate for the first three months, and individual results vary from patient to patient.
How long each medication takes to work
Mounjaro
Mounjaro starts at 2.5 mg once a week, with steps of 2.5 mg after at least four weeks on each dose. The FDA-approved maintenance doses of tirzepatide are 5 mg, 10 mg and 15 mg once weekly, with 5 mg being the lowest maintenance dose. Our guides to your first month on Mounjaro and to Mounjaro results after two months cover the early weeks. Our Mounjaro dosage guide explains each step.
The Wegovy injection
The Wegovy injection starts at 0.25 mg once a week, with at least four weeks at each dose before the next step. For adults and adolescents aged 12 and older, the US prescribing information gives 2.4 mg as the recommended maintenance dose and 1.7 mg as an alternative maintenance dose. Our Wegovy dosage guide sets out each step.
Ozempic
Ozempic is approved for type 2 diabetes, and Wegovy is the semaglutide medication approved for weight management. At Endocare, Ozempic is considered for weight management only in patients with type 2 diabetes or prediabetes. Ozempic is not approved for weight management or for prediabetes, so using it for weight management outside the treatment of type 2 diabetes, including in prediabetes, is off-label. Ozempic contains the same active ingredient as the Wegovy injection. It starts at 0.25 mg once a week, and the prescribing information directs an increase to 0.5 mg after four weeks. Our Ozempic dosage guide explains the dose steps.
GLP-1 tablets
The Foundayo prescribing information states that orforglipron, the active ingredient in this once-daily tablet, reaches its maximum concentration four to eight hours after a dose. Steady levels follow after around a week of daily doses. Our guide to your first month on Foundayo explains the starting dose of 0.8 mg and what to expect. The Wegovy pill starts at 1.5 mg, with at least one month at each step. Our article on GLP-1 pills explains how the tablets available in the UAE compare.
What your endocrinologist checks at each follow-up
Monthly follow-up appointments can be held in person at the clinic or online. At each follow-up, your endocrinologist will review your weight, any side effects and whether to change your dose. Endocare’s doctors are always available to support patients with advice.
At Endocare, body composition analysis is included free of charge at every consultation. Body composition analysis estimates body fat, muscle mass and body water. Repeated measurements help your endocrinologist understand how your body is changing beyond the number on the scale.
Frequently asked questions
Do weight loss injections work immediately?
Not fully. Mounjaro, Wegovy and Ozempic reach their peak level in the blood within around three days of an injection. This describes how the medication is absorbed, and it does not show when appetite or weight will change. Appetite may change within the first days or weeks, and weight changes typically take longer. Any dose increase is agreed with your endocrinologist, one step at a time, over several months.
Can you lose weight on the starting dose?
You can, but the starting dose is a step in the dose escalation, not a maintenance dose. The prescribing information sets an increase after the first four weeks, and your endocrinologist will review your response at each monthly follow-up.
How do I know if my weight loss injection is working?
Signs can include a smaller appetite, feeling full sooner and a gradual fall in weight. Short-term changes on the scale are often influenced by body water, alongside normal day-to-day variation. Your endocrinologist will look at the trend over several weeks, together with your body composition analysis.
Will increasing the dose faster make the injection work sooner?
We do not recommend increasing the dose faster than your endocrinologist advises. The labels set at least four weeks on each dose to reduce the risk of nausea and other digestive side effects. Never increase your dose without speaking to your endocrinologist.
Why am I not losing weight in the first month?
Some patients take longer to respond, and the first month is spent on the starting dose. If your weight is not changing despite a consistent plan, it may be worth reviewing both the plan and whether any medical factors could be contributing. Our article on not losing weight on Mounjaro covers the common reasons.
How long do you need to stay on weight loss injections?
There is no fixed duration. Your endocrinologist will agree with you how long treatment continues, based on your response and your goals. A maintenance dose is the dose that helps maintain your results once you have reached your target weight and achieved the symptom control you were treated for. Our article on maintaining weight loss explains what happens when treatment ends.
Patients should not decide by themselves to start a GLP-1 medication. A doctor’s review is critical to ensure the treatment is safe and appropriate for the individual.
At our Dubai clinic, your endocrinologist will assess you, review your blood tests and discuss whether a weight loss injection is appropriate for you. Our medical weight loss programme combines medication, where it is appropriate, with nutrition and lifestyle coaching. You can book a weight loss consultation on +971 4 285 3885 or send us a message on WhatsApp.
