GLP-1 Once a Week: Which Medicines, Why and How (October 2026)

01 · The core answer

Do you take GLP-1 once a week?

It depends on the medicine, not on the drug class. Mounjaro is a once-weekly injectable prescription medicine made by Eli Lilly, and it comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ The Wegovy injection (semaglutide) is also weekly, with pens of 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg.¹⁸ Other GLP-1 medicines are taken daily, so check the product before you assume.

If you have just been prescribed a weekly pen, pick a day that suits your routine, inject on that day each week, and keep to it. If you are comparing medicines, the dosing rhythm is one factor among several, alongside eligibility, how you tolerate each medicine, and cost.

Which one is right for you is a prescriber decision. They will look at your health, your other medicines and your routine.¹¹ If a weekly injection suits you, the Mounjaro pen costs £169.99 per month at the 2.5mg starting dose, and a new customer's first 2.5mg pen is £129.99 with code FIRST40. Prices were checked 11 October 2026.

02 · Your decision

Is a weekly schedule right for you?

A weekly schedule suits most people who prefer to think about their medicine once, not every morning. There is no daily fasting window to plan around, no tablets to remember, and the pen is used on a set day. The trade-off is that you are injecting, which some people find off-putting at first. Needles, a sharps bin and injection guidance are included with every order from us.

A daily tablet may appeal if you dislike needles. If you are unsure, read our guide on whether Mounjaro is a weekly injection, then explore our weight loss clinic for the next step. A free online consultation is reviewed by a GPhC-registered prescriber, so you do not have to decide alone.

03 · Why weekly works

Why do you only take GLP-1 once a week?

You take it once a week because the medicine stays active in your body for long enough to cover the whole interval. For tirzepatide the figure is clear: 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

That slow clearance is why a single weekly injection can keep a steady level in the body. Each new dose tops up what is left from the last one, which also explains why the effect is smooth rather than switching on and off between injections.

The medicine works by activating gut-hormone receptors. Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹ In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.

That dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic). Both are still weekly injections, so the schedule is the same even though the pharmacology differs. 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.

See our guide to weekly GLP-1 dosing for more.

04 · Taking your weekly dose

How weekly dosing works day to day

Weekly dosing means choosing one day and sticking to it. Pick a day you can remember, such as the day your week starts or the day you do your food shop, and set a phone reminder. Many people also use a companion app: our free GLPTrackr app tracks a GLP-1 journey on iOS and Android.

Mounjaro is injected under the skin once a week into 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, rotating the site with each dose. Follow the pen's instructions rather than a general rule from the internet, because pen designs differ between medicines. The same applies to storage. Once in use, a pen can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away; unopened pens go in the fridge until first use and keep until the printed expiry date.¹³

How the dose builds up

You do not start at the top dose. Mounjaro starts at 2.5mg and your prescriber steps you up through the strengths gradually, depending on how you respond and tolerate it. If you step up after 4 weeks on each of 2.5mg, 5mg, 7.5mg and 10mg, your first four pens cost £959.96 at standard prices. A new customer's first order is £40 less, and every later order is £25 less.

Wegovy's injection ladder is similar in shape: 0.25mg, 0.5mg, 1mg, 1.7mg and then 2.4mg, stepping up after at least four weeks and reaching the 2.4mg maintenance dose from week 17.¹⁸ The 2.4mg dose is the licensed maintenance dose for weight management.

05 · Missed or extra doses

What if you take GLP-1 more than once a week, or miss a dose?

Do not take extra doses to compensate, and do not take a dose early because you feel the effect has worn off. The licence is for one injection a week. If you miss a dose, 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.¹³ Our pages on taking GLP-1 more than once a week and Mounjaro more than once a week go into the detail.

If you use more Mounjaro than you should, talk to a doctor immediately. If you cannot keep fluids down, contact your clinical team — dehydration needs medical help straight away.

Twice a week and other shortcuts

Splitting the dose across the week is not how the medicine is licensed: the licence is for one injection a week. If your appetite returns before the next injection, speak to your prescriber. Read our guide on taking GLP-1 twice a week for more.

A plateau is not a reason to double doses or add unlicensed products.

Sporadic use

Taking GLP-1 sporadically, skipping weeks and restarting, is not how the medicine is studied or licensed. A long gap is a conversation for your prescriber, who will advise on how to restart.

06 · Daily alternatives

Daily GLP-1 options: tablets and liraglutide

Not every GLP-1 medicine is weekly, and the newest options in the UK are daily tablets. Wegovy tablets contain semaglutide, the same active ingredient as the Wegovy injection, taken as one tablet once a day. The routine matters: the tablet must be taken on an empty stomach after fasting for at least 8 hours, swallowed whole with a sip of water (up to half a glass, about 120ml), and you then wait at least 30 minutes before eating, drinking or taking other tablets.²⁰ If a dose is missed, skip it and take the next tablet the following day.

Foundayo contains orforglipron, a once-daily GLP-1 tablet made by Eli Lilly, the maker of Mounjaro. Unlike Wegovy tablets it can be taken at any time of day, with or without food and without water restrictions; the tablet is swallowed whole.²¹ If a dose is missed, take it as soon as possible, but never more than one tablet a day.

See current prices on the Wegovy pill and Foundayo pages.

Tablets versus a weekly injection

Mounjaro is a once-weekly injection; Wegovy tablets and Foundayo are once-daily tablets. No trial has compared Mounjaro directly with either tablet, so results from separate trials — with different people, durations and doses — should not be set against each other as if they were head to head (SURMOUNT-5 is the trial that compared tirzepatide directly with injected semaglutide). The practical differences matter as much as the averages: Wegovy tablets need a strict empty-stomach routine every morning, Foundayo has no food or water rules, and Mounjaro needs one injection a week.

Foundayo may make oral contraceptive pills less effective: switch to a non-oral method or add a barrier method for 30 days after starting and for 30 days after each dose increase. Your prescriber will go through this with you.

Liraglutide (Saxenda, and products such as Erly) is supplied at 6mg/ml and is a daily injection, unlike once-weekly Mounjaro and Wegovy.

07 · Short-term and temporary use

Can you take GLP-1 for a few months, or is it temporary?

You can, but a short course is not what the licensed treatment is designed around. Mounjaro is licensed for weight management in adults, used alongside a reduced-calorie diet and increased physical activity.¹ In SURMOUNT-1, trial figures were measured at 72 weeks, which is why prescribers talk about months and years of treatment, not weeks.

Stopping is your decision, made with your prescriber. After a final dose the medicine clears over about four to five weeks, and nothing needs doing while it clears. In SURMOUNT-4, people who stopped tirzepatide after 36 weeks regained on average 14% of body weight over the following year, while those who continued treatment lost a further 5.5% on average. Stopping should always be planned with your prescriber, with diet and activity habits ready to carry the load.

Treatment is also reviewed. If you have lost less than 5% of your starting weight after 6 months on the highest dose you can tolerate, your prescriber will discuss whether continuing or stopping is right for you.¹¹ Our aftercare includes ongoing monthly reviews, dose titration and follow-up assessments by the prescribing team, and repeat orders re-check suitability, with no auto-shipping.

Why a few months can be disappointing

Three months in, most people are still on the lower rungs of the dose ladder, so trial-average losses at this stage are modest compared with the headline figures.

08 · How fast it works

Does GLP-1 start working immediately?

Some people notice appetite change straight away; others do not until a higher dose, and both are normal. The 2.5mg starting weeks are about adjustment, and experiences differ widely: some people notice appetite change and early loss in week one, others feel little until a higher dose. Early loss includes water weight, so the trend over weeks matters more than any single weigh-in.

Weight loss on Mounjaro is gradual by design. The first weeks on 2.5mg are an adjustment phase and losses are usually modest; most measurable progress builds from 5mg onward, month by month. Think in months, not days, and judge progress by trend.

How much weight in the first months?

The honest answer is: modest. A sensible 3-month expectation on a standard titration is mid single digits as a percentage of body weight, with wide individual variation. Slower early progress does not predict failure — the dose you respond to may still be ahead of you.

For the full-length picture, here is the headline trial result. In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.² These are trial averages — individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.

Weight is not the only measure. In trials, weight loss on tirzepatide came with average improvements in waist size, blood pressure, cholesterol and blood-sugar measures, and most participants with prediabetes returned to normal blood-sugar levels.²

Plateaus

Weight loss on Mounjaro is not linear — plateaus of a few weeks are normal and expected as the body adapts to a lower weight. Within the licence, the responses are: review food intake honestly, protect protein and activity, check the basics such as sleep and alcohol, and discuss with your prescriber whether a dose step-up is appropriate if you are not yet at maximum.

09 · Risks and side effects

What are the potential dangers of taking GLP-1 medication?

Like any prescription medicine, GLP-1 treatment has side effects, and most are digestive and appear around dose changes. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.¹³ Dose increases can bring them back for a while.

For tablets, the pattern is similar. The most common side effects of Wegovy tablets are digestive — nausea, vomiting, diarrhoea, constipation, indigestion and stomach pain — along with headache and tiredness; gallstones and hair loss are listed as common.²²

Tell your prescriber about everything you take and your full medical history. That is why Mounjaro is supplied only after an online consultation reviewed by a GPhC-registered prescriber. Mounjaro is not suitable for everyone. You should not take it if you are allergic to tirzepatide or any of its ingredients, and it should not be used during pregnancy or while trying to conceive. Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive. Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are absorbed: switch to a non-oral method, or add a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase. Tell them about every medicine you take, including any diabetes treatment, because doses of some of these may need adjusting.

If you notice a new symptom, speak to your prescriber, and report suspected side effects through the MHRA Yellow Card scheme.¹⁹ For severe or persistent symptoms, get medical help straight away.

Beware cheap sources

Weekly pens are a target for counterfeits and unregulated sellers. Never buy from anyone offering to supply without a consultation or prescription. Check that a pharmacy is on the GPhC register; ours is GPhC 9012878. Our Mounjaro comes through official LillyDirect supply, direct from Eli Lilly's UK distribution, as genuine KwikPens.⁷

10 · 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

11 · NHS and private access

NHS access to weekly GLP-1 treatment

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).⁴ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

NHS access to Wegovy runs through specialist weight-management services; ask your GP.

If you go private, the process is straightforward. You complete a free online consultation, a GPhC-registered prescriber reviews it, and if they decide the treatment is not suitable, the order is refunded automatically in full. Orders placed by 3pm are dispatched the same day, with free next-day tracked delivery in temperature-controlled packaging. Saturday delivery is £14.99. The price shown is the price paid, and Klarna and pay-monthly options are available with no subscriptions.

For planning, a first year costs £2,711.88 if you stay on 5mg after your 2.5mg starting pen, up to £3,599.88 if you step up through every dose to 15mg, at standard prices. A new customer's first order is £40 less with code FIRST40, and every later order is £25 less (code DOSE25). Read our guide on whether you take Mounjaro once a week for more about the routine itself.