Your First Week on Wegovy: What to Expect

What the trial data tells us about early treatment

Clinical trials for semaglutide used a slow titration schedule deliberately. The STEP 1 study built from 0.25mg through 0.5mg, 1.0mg and 1.7mg before reaching the 2.4mg maintenance dose, spending roughly four weeks at each level. That structure exists because the side-effect burden is dose-dependent: starting low reduces the likelihood that nausea or vomiting ends treatment early. In week one, you are on the smallest dose in the schedule. The NHS semaglutide medicines page confirms this titration approach and lists the side effects most commonly reported at each stage. Most participants in the trial who experienced GI symptoms found them manageable and transient, most noticeable in the day or two after the injection, then easing before the next weekly dose. That pattern (a wave of mild discomfort after each pen, settling mid-week) is what many patients describe. Not everyone gets it. Some people feel nothing unusual at all in week one. That is also normal.

What you are unlikely to experience in week one is dramatic weight loss. The medicine takes time to reach effective concentrations and your dose is still at its lowest. Any reduction on the scales this early is more likely fluid or dietary changes than the pharmacological effect building. Week one is about adjustment, not results.

The side effects most likely to appear in the first few days

Nausea is the most commonly reported early side effect, and it tends to be mild at 0.25mg. Some people also notice constipation, loose stools, indigestion or a general feeling of fullness after smaller amounts of food than usual. Headache and fatigue can appear, particularly in the first day or two after the injection. Injection-site reactions (redness, mild soreness) occasionally occur; rotating the site between your abdomen, thigh and upper arm helps. For a full breakdown of what to expect as treatment progresses into the second month, our guide to the first month on Wegovy covers how these patterns shift.

The side effects that need same-day medical attention are different in character. Severe, persistent abdominal pain that spreads towards the back (with or without vomiting) can signal pancreatitis, which the MHRA highlighted in a January 2026 Drug Safety Update for GLP-1 medicines. Signs of an allergic reaction (facial swelling, difficulty breathing, rapid heartbeat), gallbladder symptoms such as sharp upper-right abdominal pain, and any sudden change in mood or thoughts of self-harm all require you to seek help promptly. The right place to report any suspected side effect is the MHRA's Yellow Card scheme. Do not sit on anything that feels serious.

Appetite changes: what to expect and what to eat

One of the earliest signs that semaglutide is doing something is a shift in appetite. Many patients notice they feel full faster, think about food less between meals, or find that a portion they would normally finish sits heavy after half. This can arrive within the first week, even at the starter dose, though the degree varies widely. It is one of the more welcome early signals, and also one that requires some attention. Eating smaller amounts means protein intake can quietly drop. Staying on top of hydration matters too, particularly if nausea is reducing your appetite for fluids.

Practical habits that tend to help in week one: eat slowly, stop when full rather than finishing the plate, favour protein-containing meals, and keep water nearby. Fatty or very rich foods can worsen nausea, so week one is not the time for an unusual dietary experiment in either direction. For a more detailed look at what the appetite trajectory looks like as doses increase, week five is a useful reference point, that is typically when patients are approaching or starting the 1.0mg dose and appetite suppression becomes more consistent. Understanding the broader timeline is covered in how long Wegovy takes to work.

Your pen, your first injection, and what comes next

If you are starting through a regulated online pharmacy, your first pen arrives in plain, unbranded packaging with a DPD tracking notification, nothing on the outside to indicate what is inside. The Wegovy pen is pre-filled and pre-set to the correct dose for that pen; you do not dial a dose. The injection itself is typically done into the abdomen, thigh or upper arm. The first-day guide walks through the injection process in more detail if this is your first time using a subcutaneous pen.

After week one, your next injection is seven days later at the same dose. You stay at 0.25mg for four weeks in total before your prescriber considers moving up. That pacing is not bureaucratic caution; it reflects what the clinical data says about tolerability. If you are curious how the longer arc of treatment looks, the broader Wegovy overview maps out the titration schedule and what each phase tends to feel like. Questions about cost or what is included in a private prescription are covered on the Wegovy prices page. And if you are weighing up whether this treatment is the right fit before committing, the weight-loss treatments overview sets out how the licensed options compare.