What happens after your first Wegovy injection?

Will you feel anything on the day of your first injection?

For most people, day one passes quietly. The injection itself is straightforward (a small pre-filled pen into the abdomen, thigh or upper arm) and any local sensation at the site usually fades within minutes. Some people feel a faint nausea in the hours after, particularly if they have eaten a large meal beforehand; others notice nothing at all. That variability is normal and does not predict how well the treatment will work.

The reason the starting dose is set at 0.25 mg is specifically to keep early side effects to a minimum. It is the adjustment period, not the point at which appetite suppression is expected to be strong. Think of it less as week one of weight loss and more as the body's introduction to a new mechanism. The NHS patient information for semaglutide confirms that the lower starting doses are titration steps, not therapeutic targets.

If you want a fuller picture of what to expect on your first day of Wegovy, including how to prepare and what sensations are considered normal, our dedicated guide walks you through it in detail. Symptoms that are severe, persistent beyond a couple of days, or accompanied by sharp abdominal pain that spreads to the back need prompt medical attention, that pattern can signal pancreatitis, a known but uncommon risk. Ring 999 or go to A&E if pain is severe.

What changes during the first week after the shot?

This is a question our prescribers hear most weeks, and the honest answer is: appetite tends to shift before weight does. Many people describe feeling fuller after smaller portions by day three or four, or finding that food they usually looked forward to simply seems less appealing. That is semaglutide beginning to slow gastric emptying and influence appetite-regulating pathways in the brain, the mechanism the Wegovy overview on our treatment page explains in detail.

What you are unlikely to see in week one is a noticeable change on the scales. The body does not work that quickly, and expecting dramatic early results sets up unnecessary disappointment. The first week on Wegovy is mainly about noticing early appetite signals and keeping track of how your body is responding, useful information for your next prescriber review.

GI side effects (nausea, looser stools, some belching) are most common in the 24 to 72 hours after the first injection and after each subsequent dose increase. They are not a sign that treatment is not working; they are a known feature of the titration process. Headache and mild fatigue are reported less often but do occur. Keeping a brief symptom note on your phone helps when you check in with your clinical team.

How long before Wegovy's effects really take hold?

The STEP 1 clinical trial (a large 68-week study published in the New England Journal of Medicine) found that participants taking semaglutide 2.4 mg lost an average of around 15% of their body weight. That result built up steadily over more than a year, with the maintenance dose not reached until week 16 of the titration schedule.

In practical terms, most people reach a dose where appetite suppression becomes clearly noticeable somewhere around weeks four to eight, as the dose steps upward. Weight loss that is visible on the scales tends to become consistent from around month two or three. The timeline for Wegovy to take effect varies between individuals depending on metabolic rate, dietary changes, activity and which dose they have reached.

Patience is not just advice, it is built into how the medicine is designed. Rushing through the titration or measuring success by week two misreads what the treatment is doing. If you are unsure how things are progressing, your prescriber is the right person to ask. You can also explore what the first month on Wegovy typically looks like for a broader picture of the early treatment arc.

Is there anything to watch for that would need medical advice?

Most of the first-shot experience is unremarkable. But a small number of people do have reactions that deserve attention rather than a wait-and-see approach. Seek medical help promptly for: severe stomach pain radiating to the back (pancreatitis); signs of an allergic reaction such as rash, swelling or difficulty breathing; significant vomiting or diarrhoea leading to dehydration; or any rapid heart rate or pounding in the chest. The MHRA's Yellow Card scheme at yellowcard.mhra.gov.uk lets you report suspected side effects, which helps regulators monitor safety signals across the wider population using the medicine.

Wegovy is not recommended during pregnancy, while breastfeeding, or if you are trying to conceive. Under-18s are not licensed to use it. Anyone with a personal or family history of medullary thyroid carcinoma or a condition called MEN2 should discuss this with a prescriber before starting.

If you are considering treatment and want to understand whether it is clinically suitable for you, a free consultation with our prescribers is the right place to start. There are no fees for the assessment itself, and you will hear from a qualified clinician (not an automated system) on the day you apply. For context on private treatment costs, our guide to Wegovy pricing in the UK explains what typical private prescriptions include and how to read a quoted price properly.