Semaglutide preparation: what to do before your first dose

The biggest misconception: preparation ends when the pen arrives

A lot of people assume that getting started with semaglutide is simply a case of receiving the pen and injecting on day one. In practice, the preparation that happens in the days before (and in the first few weeks of treatment) has a significant bearing on tolerability and, ultimately, how far treatment goes.

The medicine works by activating GLP-1 receptors in the gut and brain, slowing how quickly food leaves the stomach and dampening appetite signals. That mechanism is exactly why early side effects are almost always gastrointestinal: nausea, loose stools, bloating or reflux, usually peaking in the days after a new dose and then settling. None of that is a surprise if you know it is coming. The NHS medicines page on semaglutide describes this profile clearly, and it is worth reading before dose one rather than after.

The misconception matters because people who arrive at their first injection without any dietary adjustment often have a rougher first fortnight than they need to. Eating to a routine, reducing very fatty or large meals in the days before starting, and committing to steady fluid intake through the day are all low-effort steps that cost nothing but make a meaningful difference. Think of it as setting the conditions for the medicine to do its job without your digestive system working against it.

What your prescriber needs to know before semaglutide starts

A question our prescribers hear most weeks is: "do I need to stop any of my other medicines?" The answer is almost always no, but there are important nuances that make a thorough medicines review genuinely necessary rather than just a formality.

Oral contraceptives are the most time-sensitive consideration. Because semaglutide slows gastric emptying, absorption of the combined pill may be reduced in the early weeks of treatment. NHS England's guidance on weight management injections advises adding a barrier method for the first four weeks of each dose if you rely on an oral pill. This applies to semaglutide specifically in the context of any uncertainty; discuss your contraception at consultation so your prescriber can advise on your individual situation.

Other things worth listing before you start: any history of pancreatitis, gallbladder disease or personal or family history of medullary thyroid cancer, plus any supplements or over-the-counter medicines you take regularly. These are not automatic exclusions; they are the clinical picture a prescriber needs to make a genuinely individualised decision. If you are considering semaglutide for weight management and are uncertain how your health history fits, that conversation is exactly what the consultation is for.

For those moving across from reading about the European assessment, the semaglutide EPAR overview gives additional regulatory context on how the medicine was evaluated before UK approval.

Storage, injection technique and the days before your first dose

Wegovy pens must be kept in the fridge between 2°C and 8°C from the moment they arrive. Take the pen out roughly 30 minutes before you intend to inject, injecting cold liquid into the skin is more uncomfortable and, for some people, increases local site reactions. Beyond that preparation detail, the Patient Information Leaflet specifies the exact window during which a pen can be kept at room temperature; follow that, not a general rule, because the window is specific to Wegovy's formulation.

Injection sites are the abdomen, upper thigh, or upper arm, rotated each week. Rotating matters practically: injecting the same spot repeatedly over weeks can cause localised changes under the skin that affect how consistently the medicine is absorbed. Clean the site, pinch the skin gently if needed, inject at a 90-degree angle and hold for a few seconds before withdrawing. The pen's mechanism does most of the work.

Understanding the practical side of Wegovy preparation before starting means fewer surprises at the injection itself. If you want to read the fuller picture of the Wegovy treatment pathway, our Wegovy overview page covers the dose schedule, the evidence behind it and what the titration journey typically looks like.

Diet, lifestyle and setting realistic expectations before you begin

Semaglutide is licensed alongside a reduced-calorie diet and increased physical activity, not as a standalone treatment. Preparation, then, includes thinking about those two pillars before the first injection rather than after appetite begins to fall.

The appetite reduction that comes with the medicine can be sharp in some people, which creates a specific risk: eating very little of almost anything, rather than eating less of a balanced diet. Protein adequacy, fibre and hydration become more important as portions shrink, not less. Starting with a loose framework for meals (not a rigid plan, but an intention around protein sources and vegetables) means appetite reduction works with your nutrition rather than against it.

The STEP 1 trial, published in the New England Journal of Medicine, showed an average body-weight reduction of around 15% over 68 weeks at the 2.4mg maintenance dose, with participants receiving lifestyle counselling alongside treatment. That context matters: the results were not produced by the medicine alone. Our guide to preparing for Wegovy goes further into what a realistic start looks like week by week.

Cost is a practical consideration too. If you are still weighing up whether private treatment fits your situation, our Wegovy cost page sets out what is included in a transparent private prescription price and the context behind current market pricing. When you are ready to take the next step, you can speak to our prescribers through a free consultation, reviewed the same day by a GPhC-registered Independent Prescriber, not a queue for software.