What to expect in your first month on GLP-1 medication

Most patients who stop GLP-1 medication early do so in the first six weeks. Almost always the reason is side effects that would have settled if they had been managed slightly better or tolerated slightly longer. We write this article so you know what to expect and how to make the first month as manageable as possible.

Week 1: your first injection

You will have been prescribed the starting dose (Mounjaro 2.5mg or Wegovy 0.25mg). You inject once weekly on the same day. Most patients pick a Sunday evening so the strongest effects fall during a rest day.

What you will feel: very little at first. The starting dose is a tolerance dose, not a therapeutic one. It exists to let your body get used to GLP-1 signalling. You may feel a small reduction in appetite, particularly in the evening. You may notice food feels slightly more filling. You may feel nothing at all.

What you should notice: no significant nausea, no unusual gastrointestinal symptoms, no injection-site reaction worse than a small red mark. If any of those are significant, message us.

Weeks 2-4: dose building and early side effects

Around week 3 you escalate to the next dose (Mounjaro 5mg or Wegovy 0.5mg). This is when most patients start to feel the medication working and also when side effects become most noticeable.

What patients commonly describe:

A clear reduction in food noise and hunger between meals.

Smaller portions feeling satisfying. Meals that previously were too small now feel plenty.

Reduced pull towards sweet or heavy food.

Occasional nausea, particularly in the 12-36 hours after injection. Most common in the middle of the week.

Mild constipation. This is the single most common side effect and the one most patients underestimate.

Mild fatigue in the first 48 hours after injection.

Reduced tolerance for alcohol. Many patients describe feeling drunk on much less than usual.

The side effects, ranked by frequency

Nausea (affects 60-70 percent of patients in the first month): worst in the 12-48 hours after injection. Usually settles by week 4 as your body adapts. Management: eat smaller, more frequent meals; avoid ultra-processed or fatty foods in the 24 hours after injection; ginger tea helps some people; anti-emetics are available if severe and we will prescribe them.

Constipation (50-60 percent): often worse than the nausea in week 2 onwards. Gastric slowing plus reduced food intake plus reduced fluid intake is the classic trio. Management: drink more than you think you need (2.5 litres a day minimum); fibre (psyllium husk, flaxseed, oats, vegetables); daily gentle movement; laxatives (senna, lactulose) are fine short-term if needed.

Reflux (30-40 percent): slowed gastric emptying means food sits in the stomach longer. Management: smaller meals, sit up for 2 hours after eating, raise the head of the bed, omeprazole short-term if needed.

Fatigue (20-30 percent): usually transient, worst in the first week. Management: rest, hydration, stable sleep schedule.

Headaches (15-20 percent): often linked to dehydration or skipped meals. Management: regular fluid intake, do not go more than 4-5 hours without a small meal or snack.

Injection-site reactions (10 percent): usually a small red mark lasting 1-2 days. Management: rotate injection sites, leave at least an inch between weekly injections.

What we want you to do differently in month one

Three things that help every patient:

Increase your water intake. Most people on GLP-1 medication are mildly dehydrated in the first two weeks because they feel less thirsty. Dehydration worsens almost every side effect. Aim for 2.5 litres per day.

Do not skip meals. The reduced appetite makes this tempting. Skipping meals makes nausea worse, not better, and also causes a rebound of intense hunger when you do eat. Three modest meals a day is better than two large or one small.

Front-load the protein. Your reduced appetite means you will eat less total food. Protein should get priority because it keeps you full and prevents lean-mass loss. Aim for 1.2-1.5g per kg of bodyweight per day (around 80-100g for most adults).

Red flags that mean contact us immediately

Most side effects are uncomfortable but not dangerous. Some are. Message us the same day if any of the following:

Severe persistent vomiting (cannot keep fluids down for 24 hours).

Severe abdominal pain, particularly upper-abdominal pain radiating to the back (possible pancreatitis).

Signs of dehydration: dizziness on standing, very reduced urine output, confusion.

Severe headache with visual changes.

Allergic reaction: rash, wheezing, face swelling.

Blood in stool or vomit.

These are rare but important. Your monthly subscription includes unlimited messaging to your clinician and we respond to urgent messages within hours.

What we expect to see at your month-one review

Weight loss: typically 2-4kg in the first month. Less is not a treatment failure.

Appetite change: clear reduction in food noise.

Tolerance: side effects peaking and starting to settle.

Physical parameters: blood pressure, heart rate, weight, all stable or improving.

Based on how the month has gone, we either continue with the scheduled titration or hold the dose for longer. We never push the dose up if you are struggling with side effects. There is no prize for escalating fastest.

The honest bottom line

The first month is physically the hardest part of treatment. By month three you will have adapted. By month six the medication will feel routine. Getting through the first four weeks well is the single biggest predictor of how long you stay on treatment and how much weight you ultimately lose.

Ready to start?

If this article has made you think medication might help, the next step is a short consultation with one of our weight-management doctors.

Begin your consultation at this link. Online in 30 minutes, or in person at Westfield London.