Blisters From Weight Loss Injections: What To Do (October 2026)

01 · Act first

What to do if you have a blister after a weight loss injection

Leave the blister alone, protect it with a clean dry dressing if it is rubbing, and contact your prescriber or a pharmacist the same day. Do not pierce it, scratch it or put creams on it unless a clinician tells you to. A blister is a fluid-filled raised area of skin.

Before you call, gather what the reviewer will want. Take a clear, dated photo now and another each day, so changes are visible. Write down the injection date and site, which pen and dose you used, and any new products on your skin. Keep the pen, its box and the pharmacy label. If you are an EverydayMeds customer, our prescribing team can review this as part of the ongoing side-effect support that comes with your treatment.

Check the side-effect section of your patient information leaflet.¹³ It lists the reactions known for the medicine and tells you which symptoms need urgent attention. The Summary of Product Characteristics gives the same information in clinical language.¹ Neither replaces someone examining your skin.

If you are unsure which row fits, treat it as the more serious one and ask.

02 · Safe supply

Getting weight loss injections from a regulated pharmacy

If you are still choosing a supplier, a blister is the kind of problem where having a reviewable, regulated source matters. EverydayMeds is a GPhC-registered UK online pharmacy (registration 9012878), and Mounjaro comes through official LillyDirect supply, direct from Eli Lilly's UK distribution. Each order includes needles, a sharps bin and injection guidance, and our team provides ongoing monthly reviews and side-effect support.

Ordering works in three steps. First, complete the free online consultation. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. Third, our registered pharmacy dispenses and dispatches the same day if you order by 3pm, with free next-day tracked delivery in temperature-controlled packaging. For the wider picture, see our guide to buying weight loss injections in the UK.

03 · Blister, bump or bubble

Blister, bump, lump or bubble: what is the difference?

People use these words loosely, and the difference matters when you describe the problem to a clinician. A blister is a raised pocket of fluid under a thin layer of skin, and it may look clear or cloudy. A bump is a raised area that is solid, often red or pink. A lump is deeper and can feel firm under intact skin. A bubble under the skin usually means a soft, raised swelling, which is how many people describe it after an injection.

The distinction helps because each description sends a clinician in a different direction.

Give the size in centimetres or compare it with a coin. Say whether the skin is broken, whether it is clear or cloudy inside, and whether it is hot, painful, itchy or numb. Say how long after the injection it appeared and whether it is changing hour by hour. Note which injection site you used: the stomach, the front of the thigh or the back of the upper arm.

The UK Mounjaro patient leaflet lists injection-site reactions and allergic reactions such as rash, itching or eczema as common side effects (up to 1 in 10 people), and injection-site pain as uncommon (up to 1 in 100).¹³ Read it with the pen in front of you. If what you see does not match anything in the leaflet, that is not reassurance. It is a reason to ask your prescriber rather than wait.

The same approach applies whichever injectable you use, whether Mounjaro, Wegovy or another product. Each has its own leaflet, and our Wegovy weight loss injections guide covers that medicine's dosing.

Photograph the area in good light with a coin or ruler beside it for scale. Take the first photo before you apply anything, and repeat it at the same time each day. A short series of photos is more useful to a clinician than a verbal account, especially when a telephone or online review is the first contact.

If you cannot tell whether what you see is a blister, a lump or a bruise, say so. An honest "I'm not sure" is more useful than a guess, and the person reviewing it can ask the right follow-up questions. If you have more than one mark, photograph each separately and label them by injection date.

04 · The first 24 hours

The first 24 hours: a practical checklist

The first day is about protecting the skin, recording what you see and getting a professional opinion. Work through these steps in order.

• Leave it intact. Do not pop, pierce or peel a blister. Intact skin is a barrier, and breaking it adds a risk that was not there before.
• Keep it clean and covered if needed. A clean, dry dressing can stop clothing rubbing. Avoid perfumed products, new creams and home remedies on the area.
• Photograph and date it. Photograph it today, and again at the same time tomorrow. Use the same lighting.
• Keep the evidence. Do not throw away the pen, its box or the pharmacy label. The reviewer may want the product name, dose and batch information.
• Record the context. Note the injection time, the site, whether you used an alcohol swab or plaster, and any new soap, washing powder or skincare.
• Make contact. Call or message your prescriber or pharmacist the same day. If the area is spreading, hot, oozing pus or you have a fever, get medical help straight away through NHS 111 or 999 instead of waiting for a reply.

EverydayMeds support is available Monday to Friday, 9am to 5pm, by email at support@everydaymeds.co.uk, through the account portal chat or by phone on 0333 207 0413. Outside those hours, NHS 111 is the route for anything that cannot wait.

Do not inject into the affected spot again while it is still marked. Whether to use another site on your next scheduled date, and whether to delay that dose, is a decision for the clinician who has seen the photos or the skin.

Do not stop being alert after the first day. Reactions can change over the following days, and a mark that looks minor on day one can look different on day three. Keep up the photo series and update whoever is reviewing it.

Finally, report it. The MHRA Yellow Card scheme accepts reports from patients as well as clinicians.¹⁹ A report helps the regulator spot patterns, and filing one does not replace contacting your prescriber.

05 · When it is urgent

When a skin reaction after an injection is urgent

Some signs mean you should not wait for a callback. Get medical help straight away through NHS 111 or 999 if the area becomes increasingly red, hot or painful, spreads outward, weeps pus, or if you develop a fever or feel generally unwell. These are general safety signals for any skin problem, and they apply here.

Call 999 straight away if you develop swelling of the lips, face or tongue, difficulty breathing or swallowing, or feel faint after an injection. Blisters in the mouth or around the eyes, or a rash spreading across the body, also need urgent assessment. Do not drive yourself if you feel unwell.

Tell the clinician which medicine you take and when you last injected. Tell them the dose, the date and that it is a once-weekly injection. Mention any other medicines, including anything used for diabetes. Insulin and sulfonylureas, for example, may need dose adjustments alongside Mounjaro because of low blood sugar risk, so a clinician needs the full list.

The leaflet and the clinician who sees you are the right sources.¹³

If you are travelling or away from home, the same rules hold. Find an urgent care service, a pharmacy or a walk-in centre. Take your pen, box and photos, and say clearly which injectable you use. Tell the clinician it is a prescription medicine supplied by a registered pharmacy, and give the pharmacy's contact details if they want to confirm the product.

For general reassurance and context on risks, see our guide on whether weight loss injections are safe. It will not replace an assessment of your own skin, but it explains how side effects are handled.

06 · Reporting and the leaflet

Reporting a reaction: the Yellow Card scheme and your leaflet

You can report a suspected side effect yourself through the MHRA Yellow Card scheme, online or via its app.¹⁹ You do not need a diagnosis or proof that the medicine caused it. A suspicion is enough, and the report goes to the UK regulator.

Have these details ready: the medicine's brand name (for example Mounjaro), the dose and how long you have used it, the date of the injection, a description of the reaction and when it began, how it progressed, and any other medicines. The batch number on the pen or box is valuable to the regulator when it is available.

A Yellow Card report is not a complaint about your pharmacy, and it does not stop you getting treatment. It sits alongside, not instead of, telling your prescriber. Do both.

The patient information leaflet and the Summary of Product Characteristics are the authoritative documents on what is known about a medicine's side effects.¹³¹ The leaflet tells you what to do if you experience a side effect and what to tell your doctor or pharmacist. If you have lost it, the electronic medicines compendium hosts the current version.

Keep your own record as well. A note in your phone or the free GLPTrackr companion app, available on iOS and Android, can hold injection dates, sites and doses. When something unexpected happens, a record of which site you used last week is surprisingly easy to forget and very useful to a reviewer.

Finally, ask the reviewer what they want you to do next, and write it down. That should include whether to photograph, whether to attend in person, what to do on your next scheduled injection date and when they expect to hear from you again.

07 · Injection technique and sites

Injection technique, sites and rotation

Mounjaro is injected under the skin (subcutaneously) once a week, on the same day each week, at any time of day, with or without food.¹ The licensed sites are the stomach area, at least 5cm from the belly button, the front of the thigh, or the back of the upper arm if someone else gives the injection. Rotate the site with each dose.

Rotation is a basic part of the licensed instructions. Using a different spot each week avoids repeatedly injecting into the same patch of skin. A simple routine is to note each week's site, for example left abdomen, right abdomen, left thigh, right thigh, and move through them in turn. That also helps if you ever need to tell a clinician exactly where a mark appeared.

Follow the pen's instructions for use for every step of the injection, including how to attach the needle, how long to hold the pen in place and how to remove it. The leaflet and the pen's instructions are the guide for your device.¹³

The dose is set by turning the dose knob until the dose indicator shows the correct dose in the window.

Avoid areas of skin that are already marked, sore or irritated, and talk to your prescriber about using an alternative site after a reaction. Choose a site you can see and reach comfortably, and ask someone else to help if you cannot see it. The upper arm is only suitable when someone else gives the injection.

Do not alter how the pen is used to try to change the dose. Altering doses means unknown dosing accuracy and no safety data.¹

If you are new to injecting, our consultation process includes injection guidance, and each order includes needles and a sharps bin. If you have any doubt about technique, ask before your next dose, not after a problem.

08 · Pen storage and handling

Storing and handling your pen

Keep Mounjaro pens in a fridge at 2–8°C and never freeze them. Once a pen is in use, it can be kept out of the fridge not above 30°C for up to 30 days, after which it should be discarded. Keep the cap on to protect it from light, and never use a pen that has been frozen.¹¹³

Storage is worth checking if you have a skin reaction, because the reviewer will ask about it. Be ready to say where the pen was kept, whether it was ever near the freezer compartment or the back wall of the fridge, whether it was left in a car or by a window, and how long the current pen has been in use.

Do not use a pen you think has been frozen, and do not use one past the 30-day in-use window. Unopened pens should be kept in the fridge until first use and keep until the expiry date printed on the box.¹ If an unopened pen has been out of the fridge, check with the pharmacy before using it rather than relying on a remembered day limit. Figures circulating online often come from other countries' labels.

Travelling is straightforward if you plan. Carry pens in hand luggage, because hold luggage can fall below freezing, ideally in a cool bag with the prescription label or a copy of your prescription. In-use pens tolerate up to 30 days not above 30°C, so most holidays need no special arrangements. For hot climates, use an insulated pouch, and check destination rules for travelling with prescription injectables before you fly.¹

If you have any doubt about a pen's condition, keep it, do not use it and contact the pharmacy.

Our orders ship in discreet, temperature-controlled packaging by tracked next-day delivery. Put the pens in the fridge as soon as they arrive, unless you are starting that pen straight away. If a parcel arrives badly damaged, contact us within 3 days, as that is the window for reporting a faulty, damaged or wrong item.

09 · Counterfeit and unregulated

Counterfeit pens and unregulated sellers

If you have a skin reaction and bought your injection from a social media seller, a beauty salon, an unlicensed website or anyone offering to supply without a consultation or prescription, say so when you seek help. The MHRA publishes guidance and counterfeit medicine alerts, and runs the Yellow Card scheme, which accepts reports about suspect products as well as side effects.⁷

Prescription-only medicines such as Mounjaro should only be supplied after a consultation reviewed by a GPhC-registered prescriber. A seller who skips that step cannot check whether the medicine suits you, and you cannot be sure what is in the pen. Dramatic weight-loss claims, prices far below those you see elsewhere, and unbranded or repackaged pens are all warning signs.

You can check a pharmacy yourself on the GPhC register. EverydayMeds is registered under 9012878, and the register shows the pharmacy's name and status.¹² Mounjaro supplied by us comes through official LillyDirect supply, direct from Eli Lilly's UK distribution, as genuine KwikPens.

If you have used a pen from an unregulated source, do not use any further pens from it. Keep the pen and packaging, tell your prescriber or GP, and report it through Yellow Card. You can then restart treatment through a regulated route, where a prescriber assesses your suitability, sets your starting dose and follows your progress.

If you want to know more about what a regulated order involves, our weight loss injections register online page walks through it step by step.

10 · Lumps, bumps and bubbles

Lumps, bumps and bubbles under the skin

Watch it. Photograph it, note whether it is getting bigger or smaller, and note whether it is painful, hot, itchy or discoloured. A mark that is fading over the following days is a different situation from one that is growing, hardening or becoming painful. Either way, tell your prescriber at your next review, and sooner if you are worried. If a lump is accompanied by spreading redness, heat, pus or fever, treat it as urgent.

Avoid massaging, squeezing or pressing a lump unless you have been told to. Do not inject into it. Use a different site next time, rotating as the licensed instructions describe.¹

On air bubbles: people often ask what happens if a bubble is seen in the pen or injected. Follow the pen's instructions for use for preparing and checking the pen, and if you see something you do not understand, or think you have injected something other than the medicine, contact your pharmacist or prescriber. Do not try to fix a pen by taking extra or repeat doses.

The same advice applies whichever injectable you use. If you use Ozempic, Wegovy or a liraglutide product, the leaflet for that product is the right reference. Ozempic is semaglutide licensed for type 2 diabetes — it is not a UK weight-loss medicine, and a regulated UK pharmacy will not supply Ozempic for weight loss. Our site has separate material on how treatment is set up, and you can browse all weight loss treatments to compare options with a prescriber.

When to worry about any lump under the skin is a general medical question, not specific to injections. A lump that is growing, hard, painful, not settling, or that appears without an obvious cause should be seen by a doctor. If you have a lump unrelated to your injection site, do not assume the medicine is the cause and do not wait.

If a mark has not clearly improved over a few days, or you are unsure, ask for a review.

11 · Continuing treatment

Continuing treatment after a skin reaction

Whether you carry on with your next injection after a skin reaction is a clinical decision, not something to settle yourself. Contact your prescriber before your next scheduled dose. They may want to see photos, ask about the timing and appearance, and decide whether to change the site, hold the dose or stop.

If you miss a dose while waiting for advice, the licensed rule is to take it as soon as you can within 4 days (96 hours) of the scheduled time, then carry on with your usual day. If more than 4 days have passed, skip the missed dose entirely and take the next one on your normal day. Never take two doses within 3 days of each other.¹ Ask your prescriber how this applies to your situation before you decide.

You can change your injection day if needed, as long as at least 3 days (72 hours) have passed since your last dose.¹

Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹ This matters if a prescriber advises stopping: effects will wear off gradually rather than at once.

Your dose history matters too. Everyone starts on 2.5mg weekly, with increases at a minimum of four-week intervals up to a maximum of 15mg.¹ If you have recently stepped up, tell the reviewer. Do not adjust doses outside the licence on your own.

Treatment is judged over months, not days. Trials measured results at 72 weeks, and your prescriber reviews your response, including a review after 6 months on the highest dose you can tolerate.

If you are a customer, our aftercare includes ongoing monthly reviews, dose-titration and follow-up assessments with the prescribing team. Repeat orders re-check suitability, and nothing is auto-shipped, so a reaction can be raised before another pen is sent. Our guide to weight loss injections and thyroid problems shows how other health issues are handled in the same review, and our page on what to eat on weight loss injections covers the diet side while you wait.

12 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹

13 · NHS and private routes

NHS and private routes if you are worried about side effects

If a skin reaction happens, you can use either route for help, and your GP or NHS 111 can see you whether you obtained the medicine privately or not. Tell them honestly where your injection came from and what you are taking.

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first (initially BMI 40+ with four or more qualifying conditions).⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

Privately, Mounjaro is licensed for weight management in adults with a BMI of 30 or above, or a BMI between 27 and 30 with at least one weight-related condition. It must be used alongside a reduced-calorie diet and increased physical activity, and a prescriber assesses your BMI, medical history and current medicines first.¹

Payment is by Visa or Mastercard, Klarna or pay-monthly options, with no subscription lock-in.

The point is that cost and speed of access should not push you towards an unregulated seller, because a reaction is much harder to deal with when nobody can verify what you injected. If you want to compare routes and brands, the weight loss injections hub sets out the options.

Refunds and returns also differ between routes. At EverydayMeds, declined consultations are refunded automatically in full. Dispensed prescription medicines cannot be returned except where an item is faulty, damaged or wrong, and you contact us within 3 days. Refunds take 5–10 working days.