What is Tirzepatide, and is it safe for weight loss?

Dr. Babak Ashrafi

Medically reviewed by

Dr Babak Ashrafi

Last reviewed: 07 Feb 2024

Tirzepatide is the active ingredient contained in Mounjaro, a weight loss and type 2 diabetes treatment. It works by mimicking 2 hormones in your body: glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1).

These hormones make your stomach empty slower and increase the production of insulin (another hormone). They also influence hunger and satiety signalling in your brain and make you feel fuller for longer. Combined, these effects help regulate blood sugar levels in people with type 2 diabetes, and can also lead to weight loss.

Tirzepatide injections (Mounjaro) are taken once a week. Whether you take tirzepatide for weight loss or to treat diabetes, you’ll need to follow a diet and exercise regime.

Mounjaro (tirzepatide) weight loss injection 2.5mg box and pen

Key takeaways

  • Tirzepatide is the active ingredient in the weight loss and type 2 diabetic treatment Mounjaro.

  • Tirzepatide weight loss injections have been approved in the UK as of the 8th of November 2023 by the Medicines and Healthcare Products Regulatory Agency (MHRA).

  • Tirzepatide can help with weight loss as it delays the emptying of your stomach, reduces appetite and hunger, and regulates blood sugar levels.

  • You can only take tirzepatide for weight loss if you have a BMI (body mass index) of 30 kg/m² or more, or between 27 and 30 kg/m² and a weight-related medical condition like high blood pressure.

  • Tirzepatide is a prescription-only medication which follows a standard dosage schedule. This means you start on a smaller dose, which you gradually increase until you reach a maintenance dose.

What is another name for tirzepatide?

Tirzepatide is available under the brand name Mounjaro, a type 2 diabetes treatment which has been approved for weight loss as well. There are also other brands available like Zepbound, but these are only on the US market.

Mounjaro is the only brand of tirzepatide you can get in the UK for weight loss. Although this is the only tirzepatide brand name for now, it’s likely more will be available in the future.

What is tirzepatide used for?

Tirzepatide is primarily used for the treatment of type 2 diabetes, controlling blood sugar levels when diet alone isn’t enough. It was also found to help those with diabetes to lose weight, so it has been trialled as a weight loss drug.

These clinical trials showed promising results, prompting the MHRA to approve tirzepatide for weight loss in the UK.

Is tirzepatide available in UK?

Yes, tirzepatide is available in the UK for treatment of type 2 diabetes and obesity. To buy it, you will need a prescription. It is only available in the form of an injection. There are no tablets containing this ingredient available yet.

What class of drug is tirzepatide?

Tirzepatide belongs to 2 different medication classes. It’s both a glucose-dependent insulinotropic polypeptide (GIP) receptor agonist and a glucagon-like peptide 1 (GLP-1) receptor agonist.

This means it acts like the hormones GIP and GLP-1 in your body.

How does tirzepatide affect your body?

Tirzepatide mimics 2 hormones, GIP and GLP-1. This causes several things to happen:

  1. Your body produces more insulin*, which lowers and regulates your blood sugar (glucose) levels.
  2. The food remains longer in the stomach, making you feel full for longer.
  3. It sends signals to the appetite and hunger centre in your brain so you don’t feel as hungry and have less food cravings.

* Insulin is a hormone produced in your body that helps to regulate blood sugar levels. It does this by signalling to your cells to take up the excess sugar in your blood, which is stored and used later as energy. People with diabetes may not produce much insulin, if any, or it may not work like it’s supposed to. This can lead to high blood sugar levels (hyperglycaemia).

Is tirzepatide injection safe?

Tirzepatide is an effective and safe treatment for both type 2 diabetes and weight loss. You should only take tirzepatide if it’s been prescribed to you by a doctor, and you should always follow your doctor’s instructions when using it. They will make sure it’s a safe and suitable treatment based on your medical history

Dr Babak Ashrafi, Clinical Lead for Service Expansion at ZAVA.

How does tirzepatide work for weight loss?

Tirzepatide lowers your appetite and makes you feel fuller for longer. It does so by mimicking 2 hormones which are usually released right after eating. These 2 hormones, GIP and GLP-1, affect certain areas in the brain, which control hunger and satiety. This leads to weight loss because you consume less food and calories. The medication is only to be used alongside a healthy diet and regular exercise.

How effective is tirzepatide for weight loss?

Studies and clinical trials have shown tirzepatide to be an effective treatment for weight loss, leading to its approval for use.

A clinical trial comparing tirzepatide to a placebo found that 89.4% of participants taking once-weekly tirzepatide injections lost at least 5% of their initial body weight. This study was carried out over 72 weeks.

The study also reported the average weight loss per dose. Compared to a placebo, taking tirzepatide clearly resulted in more weight loss.

weight loss on Mounjaro dosage chart

How much weight can you lose on tirzepatide?

You can lose a significant amount of weight by taking tirzepatide, with studies showing you can lose 16% or more of your starting weight.

However, the amount of weight you lose depends on your circumstances, how long you take it, and how closely you follow your diet and exercise plan.

Can I get tirzepatide if I don’t have diabetes?

Yes, you can also get tirzepatide if you want to lose weight for medical reasons. You’ll need to meet certain requirements:

  • Your BMI is higher than 30 kg/m2 OR
  • your BMI is higher than 27 kg/m2 and you suffer from weight-related health conditions, such as high blood pressure or prediabetes.

Tirzepatide vs semaglutide vs dulaglutide

Tirzepatide, semaglutide, and dulaglutide are all type 2 diabetes treatments that have also been found to help with weight loss. Tirzepatide is a GLP-1 and GIP receptor agonist, while semaglutide and dulaglutide are GLP-1 receptor agonists. All of these treatments work to reduce hunger and appetite by sending signals to your brain that tell you you’re full. All 3 medications are self-injected once a week. The side effects of tirzepatide, semaglutide (Wegovy), and dulaglutide are very similar, as they work almost the same way. Dulaglutide is only licensed for type 2 diabetes.

Table comparing active incidents for weight loss: Tirzepatide vs Semaglutide vs Dulaglutide

How to take tirzepatide

For tirzepatide injections to be most effective, they should be taken once a week, at around the same time. This will also make you less likely to forget about taking your medication.

Each tirzepatide injection comes in a pre-filled pen. Always check your dose before taking it. You can find detailed instructions on using your pen in the patient information leaflet.

Inject tirzepatide into your skin, avoiding muscles or veins. Use a different injection site each week, as this can reduce pain, irritation, and swelling. You can inject it into your stomach or thighs.

Mounjaro injection sites: abdomen, upper legs or upper arms

Who can take tirzepatide?

You should only take tirzepatide if you’ve been prescribed it. For weight loss, you’ll need to have a:

  • BMI of 30 kg/m² or more (obese)
  • BMI between 27 kg/m² and 30 kg/m² (overweight) and a weight-related medical condition such as high cholesterol or prediabetes

➤ You can work out your BMI using our BMI weight loss calculator.

For type 2 diabetes, different criteria apply. This will be determined by your doctor.

When is the best time to take tirzepatide?

It doesn’t matter what time you take tirzepatide as long as you take it at the same time and day each week.

How much does tirzepatide cost?

One Mounjaro injection pen starts from £189.

Tirzepatide side effects

Like all medications, tirzepatide can cause side effects, whether you take it for weight loss or diabetes. The side effects of tirzepatide can be slightly different for everyone, and not everyone who takes it will get side effects.

Very common tirzepatide side effects include:

  • nausea (feeling sick)
  • diarrhoea

These tend to get better as your body adjusts to the medication but may come back when you increase your dosage. These side effects aren’t usually severe, but if they don’t go away, speak to your doctor.

Common tirzepatide side effects include:

  • stomach pain, burping or gas
  • constipation
  • reflux or heartburn
  • fast pulse
  • low blood sugar (when taken alongside some diabetes treatments)
  • being sick (vomiting)

Uncommon tirzepatide side effects include:

  • injection site irritation
  • gallstones
  • inflamed pancreas (acute pancreatitis) – which causes severe stomach or back pain that doesn’t go away

See the package leaflet for a full list of all possible side effects.

There’s a rare risk of a severe allergic reaction (anaphylaxis) when trying any new medication. If you get symptoms like facial swelling, difficulty breathing, or dizziness, call 999 straight away. For any other side effects that bother you or don’t go away within a few weeks, talk to your doctor.

Tirzepatide contraindications

Talk to your doctor before taking tirzepatide if you have:

  • problems digesting food
  • diabetic retinopathy or macular oedema (eye problems)
  • ever had pancreatitis

For any other health condition or medication, talk to your doctor.

Are there any warnings or precautions you should know before taking tirzepatide?

  1. You must talk to your doctor before using tirzepatide if you’re taking sulfonylurea or insulin, which are also type 2 diabetes treatments. Taking both at the same time can lower your blood sugar too much and could be dangerous. Your doctor may need to adjust your dose of these medications before starting tirzepatide.
  2. As tirzepatide can cause vomiting and diarrhoea, this can lead to dehydration, which may damage your kidneys. Make sure to drink plenty of fluids, even if you cannot eat. If these symptoms are severe or do not go away, talk to your doctor straight away.
  3. Tirzepatide can also affect how well your contraceptive pill works. If you take an oral contraceptive pill, you should use another form of contraception (like a condom) for 4 weeks after starting tirzepatide. Do the same for 4 weeks after each dosage increase.

Who cannot take tirzepatide?

Tirzepatide injections may not be suitable for everyone. You should not take it if:

  • you’re pregnant, want to become pregnant, or are breastfeeding
  • you’re under 18 years old
  • you have ever had an allergic reaction to any ingredients contained in the medication.

Can you buy tirzepatide online in the UK?

You can buy tirzepatide online if you’ve got a prescription for it as a treatment for type 2 diabetes. Our doctors at ZAVA can prescribe Mounjaro to you online – you just need to fill in a brief questionnaire with some health-related information about yourself. Afterwards, one of our doctors checks if Mounjaro is justified and safe for you to use. If so, you will receive the medication as well as ongoing support through your weight loss journey from us.

Is tirzepatide prescription only?

Yes, tirzepatide is a prescription only medication. This means you’ll need a prescription to get it from a local pharmacy or online.

You’ll need to answer a few medical questions, and a doctor will need to check your BMI to make sure it’s safe and suitable for you before prescribing.

Will tirzepatide be available on the NHS for weight loss?

Tirzepatide will be available on the NHS in 2024. You’ll need to make an appointment with your doctor to get a prescription. To get Mounjaro on the NHS you need to fulfil certain criteria, just like with any weight loss medication:

  • You have a BMI higher than 30 kg/m2 OR higher than 27 kg/m2 and at least 1 weight-related health condition (such as hypertension).
  • You have tried other ways to lose weight without success.
  • You don’t have any health conditions which make Mounjaro unsafe for you.
  • You receive Mounjaro as part of a specialist weight loss programme.


Tirzepatide is the active ingredient found in Mounjaro, which is used to treat type 2 diabetes and obesity. It acts by mimicking 2 intestinal hormones: GIP and GLP-1. Both hormones are usually released after eating to increase insulin levels and signal satiety to the brain. If injected once weekly, patients feel less hungry and lose weight by eating less. Tirzepatide has just been approved for weight loss in the UK and is available to buy with a prescription.

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Frequently asked questions

What countries is tirzepatide available in?

Tirzepatide is available as Mounjaro in the US and the UK. While Mounjaro is used to treat both type 2 diabetes and obesity in the UK, it’s only intended for diabetics in the US. Another medication called Zebpound, which also contains tirzepatide, is used to treat obesity in the US.

How can I get tirzepatide?

You can get tirzepatide with a prescription from your doctor. Another option is to buy it from a certified online doctor like ZAVA – by filling in a brief questionnaire, our doctors can assess if Mounjaro is safe and eligible for you. If so, you will receive the medication and ongoing support through your weight loss journey from us.

What is the best injection for weight loss?

There is no best injection for weight loss, as this depends on each individual. There are several approved and effective weight loss injections in the UK, such as Mounjaro, Wegovy, and Saxenda.

If you’re currently taking Saxenda and want to switch to Wegovy, check out our helpful switching guide.

You can also get weight loss tablets, such as Xenical, orlistat, Alli or Mysimba.

Does tirzepatide cause hair loss?

Hair loss is a possible side effect in patients using it to lose weight. This affects up to 1 in 10 people and might be related to the fast weight loss rather than the medication itself. If you do get hair loss after taking tirzepatide, this is likely to be short-term. You can talk to your doctor if you have any concerns about tirzepatide and hair loss.

What BMI is required for tirzepatide?

To take tirzepatide for weight loss, you’ll need a BMI of:

  • 30 kg/m² or more or
  • between 27 kg/m² and 30 kg/m² and a weight-related medical condition
Medically reviewed by:
Dr Babak Ashrafi Clinical Lead for Service Expansion
Accreditations: BSc, MBBS, MRCGP (2008)

Babak studied medicine at King’s College London and graduated in 2003, having also gained a bachelor’s degree in Physiology during his time there. He completed his general practice (GP) training in East London, where he worked for a number of years as a partner at a large inner-city GP practice. He completed the Royal College of GPs membership exam in 2007.

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Last reviewed: 07 Feb 2024

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