What Is the Main Ingredient in GLP-1 Medication? (October 2026)

01 · The short answer

The active ingredient in each GLP-1 medicine

The main ingredient is the active substance named on the box, and it differs by product.

Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly.¹ If you want the detail on that one product, see our guide to the main ingredient in Mounjaro.

02 · What it is made from

What is a GLP-1 drug made from?

A GLP-1 drug is made from a synthetic peptide, manufactured in a laboratory to imitate the hormone your body already makes. It is not extracted from animals or plants. Inside the pen the peptide is dissolved in a liquid, with the other ingredients listed in the patient information leaflet.¹³

For the wider explainer, see the active ingredient in GLP-1 medicines.

03 · What to do next

Is this relevant to you?

If you are comparing treatments for weight management, the ingredient matters less than whether a licensed medicine suits your health history. A GPhC-registered prescriber decides that after a free online consultation. When you are ready, you can browse our weight loss clinic.

04 · How the ingredients work

How the ingredients work

These ingredients work by acting on gut-hormone receptors that regulate appetite. Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1.¹ 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.¹ That dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic).¹

Results depend on the medicine and the person. In the SURMOUNT-1 trial, 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 and individual results vary.²

05 · Natural alternatives

Can you mimic GLP-1 naturally?

No supplement replicates a licensed GLP-1 medicine. Berberine, sometimes nicknamed the "poor man's Ozempic" or "nature's Ozempic", is a low-cost supplement with no clinical oversight. Marketing for these products often makes dramatic weight-loss claims, but they do not contain tirzepatide, semaglutide or liraglutide, and dosing is not standardised.

The same applies to psyllium husk and other fibre products. Eating regular meals with plenty of protein and fibre, staying active and sleeping well are sensible habits, yet they are not a substitute for treatment. If you are considering a supplement, ask a pharmacist or your prescriber first, especially if you take other medicines.

Beware of any seller offering to supply a GLP-1 pen without a consultation or prescription. Genuine medicines are prescription-only, and the MHRA has seized thousands of fake weight-loss pens in the UK and issued alerts after falsified Mounjaro pens were identified. Only buy from a pharmacy you can verify on the GPhC register.⁷

06 · Downsides and safety

The downsides and who it suits

The main downsides are side effects, the need for ongoing treatment and the cost of private supply. The most common side effects, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort. Side effects are most likely when starting treatment or moving up a dose, and for most people they ease within days to a few weeks.¹ If you notice a new or lasting symptom, tell your prescriber, and you can report it through the MHRA Yellow Card scheme.¹⁹

Because Mounjaro slows stomach emptying, it can affect how quickly some oral medicines are absorbed, particularly when you start treatment or increase the dose.¹ Tell your prescriber about everything you take, especially warfarin or other narrow-margin medicines, insulin, or sulfonylureas (where doses may need reducing to avoid low blood sugar).¹

After a final dose, tirzepatide takes roughly four to five weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹

07 · Choosing between them

Safest, cheaper and alternative options

No GLP-1 medicine is universally the safest, because suitability depends on your health, other medicines and goals. A prescriber weighs these up. Our guide to GLP-1 weight loss medication sets out the licensed choices, and diabetes medication GLP-1 covers the type 2 diabetes side.

On cost, Ozempic is licensed for type 2 diabetes, so it is not a like-for-like swap for weight management. For private pricing across brands, see the cost of GLP-1 medication, and for other options read about an alternative GLP-1 medication.

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.⁶

Mounjaro (tirzepatide) is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. It is used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.

08 · 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