Why you get a headache after your Wegovy shot — and what to do

The day after your injection: what is likely happening

Picture it: it is Tuesday morning, you did your shot yesterday evening, and now there is a dull pressure behind your eyes. This is something our prescribers hear about most weeks, and in the majority of cases the explanation is straightforward. Semaglutide slows gastric emptying and suppresses appetite, so people eat and drink noticeably less in the first day or two after an injection. Less fluid intake can mean mild dehydration, and that alone is enough to bring on a low-grade headache in many adults.

There is also a vascular element. GLP-1 receptor agonists like semaglutide have modest effects on blood pressure, and a small drop in blood pressure (especially if you are moving from sitting to standing quickly) can trigger a brief headache or lightheadedness. The NHS patient information for semaglutide lists headache among the common side effects that affect up to one in ten people. It tends to be most noticeable during the first few weeks and after each dose step up, then fades as your body settles.

Fatigue can add to the picture too. If you are finding tiredness compounds the post-injection headache, our guide to feeling tired after a Wegovy shot covers the overlapping reasons and practical adjustments worth trying.

Practical steps that actually help

Hydration is the most reliable lever. Aim for at least 1.5–2 litres of plain water across the day of and the day after your injection. If nausea is making it hard to drink large amounts at once, small sips every 15–20 minutes tend to work better than trying to gulp a full glass.

Eating matters too. Appetite suppression is part of how Wegovy works, but skipping meals entirely puts your blood sugar through sharper swings, and that can worsen a headache. Smaller portions eaten more frequently (something light and protein-containing) tend to help more than either forcing a full meal or skipping entirely.

Standard over-the-counter pain relief such as paracetamol can be used as directed on the pack, assuming there is no clinical reason it is unsuitable for you. Ibuprofen and other NSAIDs are worth discussing with your prescriber first if you are taking them regularly alongside Wegovy, simply because they can affect kidney function and stomach lining. Beyond medication, the basics apply: a cool, quiet room, keeping your screen brightness down, and not scheduling anything stressful for the afternoon post-injection are the kind of adjustments people find genuinely useful. For a wider picture of how headache fits into the broader side-effect profile, the full Wegovy side effects page covers the complete list with the same practical framing.

Headaches that need more than home management

Most post-shot headaches are dull, predictable and gone by the next morning. The ones that are not follow a different pattern. Get medical help the same day if your headache is:

Sudden and severe — described as the worst headache of your life, or one that came on in seconds rather than building gradually. This warrants a 999 call or immediate attendance at A&E, because a thunderclap headache can signal a serious vascular event unrelated to Wegovy.

Accompanied by visual changes, confusion, chest pain or one-sided weakness. These combinations are red flags regardless of the medicine you are taking.

Persistent beyond 72 hours without any sign of easing, especially if it is getting worse rather than better. That pattern is not typical of a post-injection side effect and deserves a prescriber's assessment.

Paired with severe stomach pain that spreads to your back. The MHRA highlighted in early 2026 that acute pancreatitis, while infrequent, is a known risk with GLP-1 medicines. Severe abdominal pain is the primary symptom to watch for; headache accompanying it is secondary, but together they signal you should not wait. The Yellow Card scheme is the right place to report any side effect you consider serious or unexpected, it feeds directly into the MHRA's ongoing safety monitoring.

If you are unsure whether your headache fits the 'wait and see' or 'seek help now' category, our prescribers are available seven days a week through aftercare. You can also explore whether headache is a recognised Wegovy side effect for a more detailed breakdown of the clinical evidence behind this symptom.

Adjusting treatment and longer-term patterns

If headaches are recurring after every injection rather than fading over the first few weeks, that is a pattern worth raising at your next clinical review. A prescriber may consider whether slowing the titration schedule would help, and our page on what to do about a headache after taking Wegovy covers how to have that conversation and what adjustments are typically considered. This is not an automatic decision to make on your own; it needs clinical input, because dose timing affects the overall course of treatment.

Some people find that switching the day of their injection shifts the headache away from days when they need to be at their best, without changing anything clinically. If you would like to read more about why this symptom occurs and how long it typically lasts, our detailed guide to Wegovy headache brings together the clinical reasoning and the practical advice in one place, and is exactly the sort of thing to mention at aftercare rather than quietly adjusting without support.

Wegovy is a prescription-only medicine and every course is individually reviewed. If you are considering starting treatment or want to discuss side effects as part of an eligibility assessment, the free consultation page is the starting point, a GPhC-registered prescriber reviews your answers the same day. For background on the treatment itself, the Wegovy treatment page covers licensing, how semaglutide works and what clinical trials showed about weight outcomes.