Your first Mounjaro injection is 2.5 mg once weekly for four weeks, then 5 mg, on Singapore's registered schedule (Singapore NDF). It goes under the skin of the abdomen or thigh, at any time of day, with or without meals (label, Singapore NDF). Injection-site reactions were reported by 6% to 8% of adults on tirzepatide against 2% on placebo (US prescribing information). Dr Quek sets your pace at GetLean.
In a post hoc analysis of SURMOUNT-1, 82% of adults who took at least 75% of their doses and stayed to week 72 had lost 5% or more of their body weight by week 12 (Ard 2025); individual results vary. What this article does not contain is the step-by-step for operating your particular pen, and the reason for that is in the section below rather than buried in a disclaimer.
In Singapore, tirzepatide is registered as Mounjaro, and semaglutide injection as Wegovy for weight management and as Ozempic for type 2 diabetes. The figures in this article are given by molecule, as the trials and product labels report them. Whichever medicine is prescribed, GetLean plans the exit from the first consultation. Coming off GLP-1 in Singapore: what happens and how to plan sets out how.
Instructions for Use: the device leaflet packed with the pen itself, separate from the prescribing information. It is written for the exact presentation you were dispensed, which is why it beats any general article, including this one.
Why the first dose is the smallest one
Because the schedule is built to start low and go up slowly, deliberately.
GLP-1 medication is not started at the dose it is intended to reach. It begins at a low starting dose and steps up over weeks, and the labels state the escalation is there to reduce the risk of gastrointestinal reactions (label). That means the first injection you give yourself is the gentlest one you will give.
Your own doses and the interval between steps come from your prescriber and your leaflet, and they differ between medicines and between people; tirzepatide's registered starting step is set out in the next section. How dose titration works explains the principle and why the ramp exists.
When does Mounjaro start working?
In a post hoc analysis of the main Mounjaro trial, 82% of adults who took at least 75% of their doses and stayed to week 72 had lost 5% or more of their body weight by week 12. Individual results vary, so how soon it works for one person is something the prescribing doctor reviews with them.
That figure comes from SURMOUNT-1, in which 1,545 of the adults treated with tirzepatide took at least 75% of their doses and were weighed at weeks 0, 12, 24 and 72; they were sorted by weight change at week 12 (Ard 2025). Of the 18% who had lost less than 5% at week 12, 90% had reached 5% or more by week 72 (Ard 2025). The first four weeks are the starting step: on Singapore's registered schedule, 2.5 mg once weekly, then 5 mg (Singapore NDF). The trial's 72-week results include a 20-week dose-escalation period (Jastreboff 2022), and the blood-level figures below measure the medicine in the body, not what a person feels.
Weeks 1 to 4. The US prescribing information states that steady-state blood levels of tirzepatide are reached after four weeks of once-weekly dosing (label). The US prescribing information for weight management gives its half-life as about 5 to 6 days in people with overweight or obesity (prescribing information). Both are measures of the medicine in the blood, not of what a person feels, so neither forecasts when an effect begins.
At each increase. Gastrointestinal reactions cluster at the increases, and tirzepatide's label states most nausea, vomiting and diarrhoea occurred during escalation and decreased over time (prescribing information). The label gives no timeframe for "decreased over time".
What the trials say about timing. A post hoc analysis of SURMOUNT-1, meaning one planned after the trial rather than before it, sorted 1,545 of the adults treated with tirzepatide by their weight change at week 12 (Ard 2025). In it, 278 adults (18%), whom the authors call late responders, had lost less than 5% of their body weight at week 12; of those 278, 250 (90%) had lost 5% or more by week 72, and the average time to reach a 5% loss was 24.8 ± 12.7 weeks (Ard 2025). It covered only adults who met the analysis criteria, so it describes what happened in that trial and is not a forecast for any one person; individual results vary.
In practice. For the weeks when eating changes, Hawker centre when you can finish only half a plate covers ordering at a Singapore hawker centre on a smaller appetite. If an injection day is missed, missed doses covers what to do. At GetLean, dose changes are made at the monthly check-in with Dr Quek, working towards the lowest effective dose; each one is his decision. Habits are built with daily WhatsApp coaching while the medication is working.
Wondering how your own first weeks will go? At GetLean, Dr Quek reviews how it's going every month and decides each dose change, so the pace is set with a doctor, not by guesswork. Book your consult to see whether Mounjaro is suitable for you.
Should Mounjaro be taken in the morning or at night?
Either works. Mounjaro is a once-weekly injection, and Singapore's product information says it can be given at any time of day, with or without meals, so choose a time and a day you can keep every week.
Singapore's product information says the dose can be given at any time of day, with or without meals, and that injection sites should be rotated with each dose (Singapore NDF). The day of the week can be changed if necessary, as long as the time between two doses is at least 3 days (Singapore NDF). If a dose is missed, it should be given as soon as possible within 4 days; after more than 4 days the missed dose is skipped and the next one is given on the regular day (Singapore NDF). The US Medication Guide says the same and adds not to take 2 doses within 3 days (72 hours) of each other (US Medication Guide). Because both documents allow any time of day, the choice is practical: many people pick a day when they are at home and unhurried, which is a preference rather than a clinical requirement. Missed doses covers what to do when a day slips. Your prescriber's instructions come first.
Whatever time you pick, Dr Quek reviews how it's going every month, and anything clinical goes to him through the care team on WhatsApp (9am to 9pm every day, Singapore time). Outside those hours an urgent symptom does not wait for a reply: go to an emergency department, or call 995 if it is an emergency. Book your consult to see whether Mounjaro is suitable for you.
Where it goes, and choosing a day
Abdomen or thigh, weekly, on a day that suits you.
Both labels name the abdomen and the thigh. They differ on the upper arm: semaglutide's names it as a site you can use yourself (label), while tirzepatide's states the back of the upper arm is for someone else to administer (label).
On timing, the labels are more relaxed than people expect. The medicine is taken once weekly, on the same day each week, at any time of day, with or without meals — and the label states explicitly that the time of day and the injection site can both be changed without any adjustment to the dose (label). Both instruct rotating the site with each dose.
So pick a day you will remember. Many people choose one where they are at home and unhurried, which is a preference rather than a clinical requirement. The site detail and the clearance from the navel are in injection sites, storage and travel.
The step that is not in this article
How the pen itself is prepared and fired.
This is not an oversight and it is not caution for its own sake. Pens genuinely differ — between the two medicines, between single-dose and multi-dose presentations, and between versions of the same product. The sequence, what you are meant to see or hear, and how long the pen stays against the skin are not the same across them.
An article that gave you one version of those steps would be right for some readers and wrong for others, and a reader who followed us instead of the leaflet in their own box would be following the wrong instructions for the device in their hand. That is a safety problem rather than a style choice, which is why the line is drawn here.
What to do instead is unglamorous and works: read the Instructions for Use that came with your pen, and ask your prescriber or pharmacist to watch you do it once. Being shown once by someone who can see your actual device is worth more than any written description of it.
Do Mounjaro injections hurt?
Most adults in the Mounjaro weight-loss trials did not report any injection site reaction: 6% to 8% of adults on tirzepatide did, against 2% on placebo. The label gives no separate pain score, so nobody can promise how an injection will feel.
"Injection site reactions" is the label's group term for events such as injection site pain, bruising, redness, itching and rash. In the pooled weight-loss trials it was reported by 6% of adults on 5 mg, 8% on 10 mg and 8% on 15 mg, against 2% on placebo (US prescribing information). The injection goes under the skin of the abdomen or thigh once a week, or the back of the upper arm if another person gives it, and the site changes with each dose (Singapore NDF). Pens differ between presentations, so the leaflet packed with yours is the instruction to follow, and asking your prescriber or pharmacist to watch you do the first injection is a reasonable request. What one person feels is not predictable from a trial average.
Nervous about the needle? Tell Dr Quek at your GetLean video consultation, and if the injections still worry you afterwards, daily WhatsApp coaching keeps you in touch with our care team (9am to 9pm every day, Singapore time), so he can hear about it early. Outside those hours an urgent symptom does not wait for a reply: go to an emergency department, or call 995 if it is an emergency. Book your consult with Dr Quek to discuss whether treatment is suitable for you.
Afraid of needles?
Say it at the consultation. That is the whole recommendation.
A concern about needles is a clinical conversation — it affects how a first dose is best approached, and it is exactly the kind of thing a doctor would rather know in advance. Raising it does not count against you, and it is not a reason to talk yourself out of an assessment. Fainting around needles is worth telling the doctor about too.
If you are wondering whether a tablet would avoid the question entirely, is there a GLP-1 that is not an injection gives the Singapore answer, which is more complicated than you might expect. If what brought you here was a search for a tablet instead, the registered picture is in the tablet, and what it is for.
The hours and days after the first dose
The effects that show up are usually digestive rather than at the injection site.
For tirzepatide, the reactions reported in 5% or more of patients include nausea, diarrhoea, vomiting, constipation, abdominal pain and indigestion, alongside injection site reactions, fatigue, hypersensitivity reactions, belching, hair loss and reflux (label). The labels instruct escalating the dose gradually to reduce the risk of gastrointestinal reactions, which is part of why the schedule starts low (label).
When they start, how long they last and how bad they get vary between people, and no trial average predicts an individual. GLP-1 side effects covers what is common and what settles, and managing nausea covers the most frequent one.
What is worth having ready
Not much, and none of it is special equipment.
Somewhere to put the used pen or needle afterwards is the one thing people are most often unprepared for, and it is worth asking your prescriber or pharmacist what they want you to do with it before your first dose rather than after. Practice on disposal differs between clinics and between countries, so this is a question for the people who dispensed your medicine rather than for a general article.
Beyond that: the leaflet, somewhere you can sit down, and a few unhurried minutes. Some people find it easier not to make an occasion of it. Others prefer to do the first one with someone else in the room. Neither is clinically better than the other.
What warrants a call in the first week
Two lists exist and neither is restated here, because splitting them across pages is how they get misremembered.
For anything at the injection site — a mark that is spreading, increasing pain, warmth, fever or pus — see bruises, marks and lumps.
For anything else — severe abdominal pain, persistent vomiting, signs of an allergic reaction — see red flags on GLP-1, which is the page that covers the rest of the body.
If something worries you and it is not on either list, that is still a reason to contact the person who prescribed it. A question that turns out to be nothing is a normal part of the first month, not an imposition.
If you have not started yet and are reading this to decide, you can book your consult and speak to a doctor about whether this is suitable for you. Questions to ask your doctor before starting Mounjaro (tirzepatide) lists what to ask first.
Read the transcript
Searches for how to inject Mounjaro have shot up in Singapore over the past year.
So what should you expect from your first injection?
It's the smallest dose: 2.5 mg, once a week, for four weeks.
So here's what I'd suggest. Three things.
One: ask to be shown. The label says your doctor should show you how to prepare the injection before your first one. And read the leaflet in your box.
Two: pick your day. Any time, with or without food. To move it, keep at least three days between doses. If you miss one, take it as soon as you can, within four days. After that, skip it.
Three: keep your fluids up. The label's most common side effects include nausea, diarrhoea, vomiting and constipation. Most of the nausea, vomiting and diarrhoea came while the dose was going up, then eased. Losing fluid that way may cause kidney problems, the label says. Tell your doctor about any side effect that bothers you.
And severe stomach pain that won't go away, with or without vomiting, sometimes through to your back? Please call your doctor straight away.
Insulin or certain diabetes pills? Ask about low blood sugar.
Got a weight goal this year? At GetLean, I'm your doctor. GLP-1 medication kickstarts it, daily WhatsApp coaching builds the habits, and we plan your way off the medication. See if you qualify, link in my profile.
Common questions
Can I inject myself, or do I need a nurse?
Both medicines are designed for self-injection at home, and the registered labels describe self-injection sites (semaglutide, tirzepatide). How your particular pen is prepared and used comes from the leaflet packed with it, and asking your prescriber or pharmacist to watch you do it once is a reasonable request.
Where should the first injection go?
The abdomen or the thigh for both medicines. The upper arm is treated differently by each — semaglutide names it as a self-injection site (label), while tirzepatide states the back of the upper arm is for another person to administer (label).
What time of day should I inject?
The registered labels state it is taken once weekly at any time of day, with or without meals, and that the time of day and the injection site can be changed without adjusting the dose (label).
Will the first dose make me feel ill?
The common effects are usually digestive rather than at the injection site. For tirzepatide, nausea, diarrhoea, vomiting and constipation are among the reactions reported in 5% or more of patients, alongside several others (label). What happens to any individual is not predictable from a trial average.
Why doesn't GetLean's first-injection article explain how to use the pen?
Because pens differ, and a general instruction that contradicted the leaflet in your box would be a safety problem rather than an inconvenience. The leaflet is written for the exact presentation you were dispensed.
When does Mounjaro start working?
In a post hoc analysis of the main Mounjaro trial, 82% of adults who took at least 75% of their doses and stayed to week 72 had lost 5% or more of their body weight by week 12 (Ard 2025). Of the 18% who had not, 90% reached 5% or more by week 72; individual results vary. The first four weeks on Singapore's registered schedule are the 2.5 mg starting step, then 5 mg (Singapore NDF); the prescribing doctor decides the pace.
What happens in the first four weeks of tirzepatide?
On Singapore's registered schedule the dose is 2.5 mg once weekly for four weeks, then 5 mg (Singapore NDF). The US prescribing information states that steady-state blood levels are reached after four weeks of once-weekly dosing (label), and tirzepatide's label states most nausea, vomiting and diarrhoea occurred during escalation and decreased over time (prescribing information). What happens to any individual is not predictable from a trial average.
Should Mounjaro be taken in the morning or at night?
Either works. Singapore's product information says it can be given at any time of day, with or without meals, once a week; choose a time and a day you can keep, and know that the day can be changed if the gap between two doses is at least 3 days (Singapore NDF). Your prescriber's instructions come first.
Do Mounjaro injections hurt?
Most adults in the trials did not report an injection site reaction: 6% to 8% of adults on tirzepatide did, against 2% on placebo, and the label gives no separate pain score (US prescribing information). What one person feels is not predictable from a trial average.