Your first month on a prescription weight loss medication may bring appetite changes, possible side effects and gradual weight loss. Here's what's normal, what isn't, and how to manage it.
Key Facts
A reduced appetite usually starts 24 to 72 hours after your first injection and peaks around days 3 to 5.
Nausea affects 18 to 32% of patients but usually settles within 2 to 4 weeks.
Average weight loss in month one is 0.9 to 2.3kg, with larger losses coming in months 2 to 4.
Light exercise is safe from week 2 but avoid high-intensity training until side effects improve.
Most side effects are mild to moderate and resolve with time as your body adjusts to the medication.
Table of Contents
What happens in week one after your first injection?
When does appetite suppression actually start?
What are the most common side effects in month one?
How much weight will I actually lose in the first 30 days?
What should I eat when I’m not hungry?
Is it safe to exercise during your first month?
What red flags should trigger a prescriber call?
Can you drink alcohol while starting treatment?
Will side effects go away or are they permanent?
Frequently asked questions
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What happens in week one after your first injection?
In the first week, you can typically expect a mild reaction at the injection site, perhaps some feelings of nausea or changes to your eating habits, and minor adjustments to your digestion. These side effects will usually go away in a few days, and weight loss may not be apparent at this stage.
The actual injection is with a very thin and short needle (like the type on an insulin pen) and many people describe it as a brief scratch, and often less noticeable than having blood taken. You inject it once a week either into your stomach, upper leg or upper arm.
Days 1 to 2: You may notice some mild redness or tenderness at the injection site. Some people feel slightly less hungry than usual, while others feel no change at all.
Days 3 to 5: Most people’s lack of appetite will be at its strongest during these days. You might also notice the first signs of fullness after small amounts of food, and maybe some nausea.
Days 6 to 7: It is normal for the effects to start to fade slightly before your next injection is due. The medication gradually builds up in your system over the first few weeks.
If you feel nothing in week 1, don’t panic. You're on the lowest starting dose, and 15 to 30% of patients experience a delayed response, which means it doesn’t kick in until weeks 2 to 3.
When does appetite suppression actually start?
You’ll generally start to have less of an appetite between 1 and 3 days after the injection, peaking at around 3 to 5 days. The medication does this by mimicking not one but two natural hormones: GLP-1 and GIP. This “dual action” helps regulate appetite and blood sugar more broadly, and it may make the medicine more tolerable for some people.
The effect of appetite suppression when you’re on the starting dose isn’t always huge. Some people will notice a clear shift in how hungry they feel, whereas others describe it as a more subtle change: ‘food noise’ is suppressed, or they feel full after eating about half as much as usual. Both of these experiences are quite typical.
Around 15 to 30% of patients experience delayed appetite suppression, with the full result not becoming apparent until weeks 2 and 3. If you’re in this group, it doesn't mean the medication isn't working: the first dose is intentionally lower, and as your dose increases over the following months, the effects will become stronger.
What are the most common side effects in month one?
In your first month, the most common side effects are gastrointestinal, and these are mild to moderate in severity for between 40 and 85% of people. Fortunately, they usually settle down in a week or so as your body gets used to the medication.
Side effect | Incidence | Peaks at | How to manage |
|---|---|---|---|
Nausea | 18–32% | Week 2 | Small meals, ginger tea, bland foods, eat slowly |
Diarrhoea | ~23% | Weeks 1–2 | Stay hydrated, avoid fatty foods, electrolyte drinks |
Vomiting | ~12% | Week 2 | Smaller portions, avoid strong smells, sip fluids |
Fatigue/dizziness | 10–15% | Weeks 1–2 | Rest, stay hydrated, avoid skipping meals |
Injection site reaction | Common | Week 1 | Rotate injection sites, apply cool compress if tender |
However, if the side effects are disrupting your day-to-day life, you should talk to your prescriber. Adjusting the timing of your injection (a lot of people prefer taking it at bedtime) or increasing the medication dose more slowly could be beneficial.
How much weight will I actually lose in the first 30 days?
People lose on average between 0.9 and 2.3kg (2 to 5 pounds) in the first 30 days, although people with a higher starting weight will experience a greater absolute loss. Don't expect to see massive changes in the first month.
The starting dose of the medication is very low while your body is still getting used to it. Months 2 to 4, as your dosage increases, is when you’ll really start to see results. In fact, in the clinical trials, 86% of participants achieved over 5% weight loss during the full trial period (72 weeks), with real momentum building from months 2 to 4 as the doses increased.
If the number on your scales hasn’t changed much in the first month, that’s perfectly normal. A slow start doesn’t mean the medication isn’t working, you’re simply in the ‘getting started’ period and it is allowing your body to prepare before the full effects kick in.
What should I eat when I'm not hungry?
Focus on food with lots of nutrients and protein, but in smaller amounts. Think eggs, Greek yoghurt, fish, chicken and beans. Fatty or very oily foods will likely make you feel even more nauseous, so these should be avoided. Sip water, broth or electrolyte drinks slowly throughout the day.
If you don’t have much of an appetite, it's tempting to skip meals entirely. However, your body still needs fuel to function and if you skip meals, you may lose muscle and feel your energy levels plummet.
To give your meals a basic structure, try to have one protein (between 20 and 40g), a serving of vegetables or salad, and a carbohydrate that releases energy slowly (like wholemeal bread, brown rice or oats). And if a normal meal feels too much, a protein shake or Greek yoghurt with berries is a perfectly acceptable alternative. It's better to have a little something than to have absolutely nothing at all.
Is it safe to exercise during your first month?
After the first 2 weeks, it is fine to do light to moderate exercise as long as it’s not too strenuous: walking, swimming and yoga are good options. However, high-intensity exercise might make you feel more nauseous or dizzy in those first weeks.
Week 1: Don’t overdo things. Gentle walks are fine, but as your body is getting used to the medicine, you’re more likely to feel nauseous from exercise.
Week 2: Slowly get back to your normal routine. If you go to the gym regularly, start at a lower intensity and gradually build back up to normal. It’s important to stay hydrated (as the medication can dehydrate you) and get enough protein both before and after a workout.
It’s also worth starting or continuing resistance training. It’s good for preserving muscle loss while you’re losing weight and is actually more important than cardio for long-term body composition. Three sessions a week, even at a moderate intensity, will have a positive overall effect.
When should you call your prescriber if you are experiencing side effects?
The symptoms felt in your first month are usually fairly mild and expected. However, if you notice certain side effects, you may require immediate medical attention.
Contact your prescriber immediately if you experience any of the following: severe vomiting (unable to keep fluids down for 24 hours), severe abdominal pain (upper abdomen radiating to the back, which could be a sign of pancreatitis), signs of an allergic reaction (rash, swelling, difficulty breathing), chest pain or shortness of breath, or persistent severe nausea for more than 2 weeks that isn't responding to typical management strategies.
It’s normal to feel nauseous, have looser than usual bowel movements, and feel tired during weeks 1 to 3, but it’s not normal to have severe or worsening symptoms. If you’re unsure about anything, it’s best to err on the side of caution and get in touch with the prescriber to talk through any concerns you have.
Can you drink alcohol while starting treatment?
Alcohol isn’t forbidden on treatment, but it’s more likely to make you feel nauseous in those first few weeks. As your stomach will be slower to empty and you’ll have a reduced appetite, alcohol can make you feel a lot worse than it normally would.
For the first couple of weeks, it’s best to not drink any alcohol at all or only have a very small amount. After the third week, having a little with food should be tolerable. You should avoid drinking on an empty stomach and especially sugary cocktails (as they’ll make any stomach or digestive symptoms worse), and drink lots of water.
Alcohol doesn’t reduce the medication’s effectiveness, but alcoholic drinks can add empty calories that could get in the way of your progress. If you have a social event coming up, try to have a meal with plenty of protein in it before you go and try to pace yourself when you’re there.
Will side effects go away or are they permanent?
As your body gets used to the medicine, most of the side effects will improve or disappear in 1 to 4 weeks. Although if you titrate up or change dose, you may experience side effects as your body gets used to this new dose. Nausea is generally at its worst around the second week, but will normally get better by weeks 3 to 4.
Real-world research shows that 20 to 50% of patients discontinue treatment within the first year, and a lot of the time this is because of side effects during those first few weeks. This is why having a prescriber who is there to support you is so important. If your side effects are really bad, changing your dose, when you take it, or switching to a different medication can really help.
The people who get through the first month with the right support almost always find the side effects manageable by the second month. So if you're struggling, don't suffer in silence – talk to your prescriber first before you decide to stop taking the medication.
Explore our range of weight loss injections and weight loss tablets.
Get £15 off your first weight loss order with code: START15.
Frequently asked questions
Will the injection hurt?
Prescription weight management injections use thin, short needles similar to insulin pens. Most of the time people have very little or no pain from them, and in fact it’s usually less painful than getting blood taken. If you’re worried about needles, numbing cream is available.
Am I a non-responder if I don't feel effects in week one?
No. Around 15 to 30% of patients find that their appetite doesn’t start to decrease until weeks 2 or 3. The effects in the first week on the starting dose might feel quite subtle. Just keep taking the medication as directed and get back in contact with your prescriber after a few weeks if you have any concerns.
Can I eat normally while on my medication?
Your appetite will be reduced, and so you’ll naturally eat smaller amounts. Instead of worrying about calorie counting, focus on getting lots of nutrients from your food, enough protein (between 1.0 and 1.6g per kg of body weight), and drinking plenty of fluids.
Is nausea the most common side effect?
Nausea affects 18 to 32% of patients and is one of the most discussed side effects; however, overall gastrointestinal changes (mild to moderate) affect 40 to 85% of patients. Fortunately, these side effects usually settle within 2 to 4 weeks.
Should I do anything special to prepare for month one?
Stock up on ginger tea, electrolyte drinks and bland snacks. Plan simple, protein-rich meals in advance. If you can, try not to make lots of social plans for weeks 2 to 3. Also, arrange a follow-up chat with your prescriber.
Can I stop if side effects are too much?
If the side effects are affecting you too much, do not stop taking the medication without first speaking with your prescriber. They might be able to change your dose, when you take it or switch you to a different medication, which may resolve the problem. Tapering down creates a much smoother transition than stopping suddenly.
How do I know if my dose is working?
A reduced appetite is the biggest sign that the medication is working. You might also experience some nausea, feel a shift in your energy levels and slowly begin to lose weight. The low starting dose may only have very subtle effects. At weeks 2 to 4, check in with your prescriber to speak about any concerns.
What happens after month one: do effects continue?
Yes, the majority of patients continue to have a lower appetite and to lose weight steadily from month 2 to 6 and beyond. Your prescriber will slowly increase your dose as appropriate.
If you’re worried about side effects or how well you’re doing during your first month of treatment, get in touch with your prescriber or pharmacist. They can adjust your treatment plan so you benefit as much as possible from the medication.
References
Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-16.
Gorgojo-Martínez JJ, Mezquita-Raya P, Carretero-Gómez J, Castro A, Cebrián-Cuenca A, de Torres-Sánchez A, et al. Clinical recommendations to manage gastrointestinal adverse events in patients treated with GLP-1 receptor agonists: a multidisciplinary expert consensus. J Clin Med. 2022;12(1):145.
Wilding JPH, Batterham RL, Calanna S, Davies M, Van Gaal LF, Lingvay I, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002.
Liu Y, Tian Q, Yang J, Wang H, Hong T. No pancreatic safety concern following glucagon-like peptide-1 receptor agonist therapies: a pooled analysis of cardiovascular outcome trials. Diabetes Metab Res Rev. 2018;34(8):e3061.
Jerlhag E. GLP-1 signaling and alcohol-mediated behaviors; preclinical and clinical evidence. Neuropharmacology. 2018;136(Pt B):343-9.
Gleason PP, Urick BY, Marshall LZ, Friedlander N, Qiu Y, Leslie RS. Real-world persistence and adherence to glucagon-like peptide-1 receptor agonists among obese commercially insured adults without diabetes. J Manag Care Spec Pharm. 2024;30(8):860-7.