How long do Mounjaro side effects last?

In this article, we will look into everything you need to know about Mounjaro, the new once-weekly injectable weight loss medication. We'll explain the common side effects associated with Mounjaro, explore how long these side effects typically last, and advise on when you may wish to seek medical attention if you experience side effects. We'll also provide information about where you can safely purchase Mounjaro online.

What is Mounjaro?

Mounjaro is a prescription-only weekly self-injected medication designed to help people lose weight when used alongside a healthy balanced diet and regular exercise, or as a treatment for type 2 diabetes (BBC, 2023). Its active ingredient is a medication called tirzepatide. Tirzepatide helps to facilitate weight loss by acting on hormones in the body, namely glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). These hormones help you to feel fuller for longer whilst also helping to regulate blood sugar levels. Mounjaro was approved for use in the UK as a weight-loss medication in February 2024.

What are the side effects of Mounjaro?

As with all other medications, using Mounjaro does come with the risk of experiencing potential side effects. Some side effects are more common than others.

Common Side Effects of Mounjaro (Tirzepatide)

Like many prescription medicines, Mounjaro (tirzepatide) can cause side effects. Most are mild, but it’s important to understand what to expect. This guide explains the common side effects for people in the UK using Mounjaro for type 2 diabetes or weight management.

Low Blood Sugar (Hypoglycaemia)

If you take Mounjaro with metformin and another diabetes medicine called an SGLT2 inhibitor, you may experience low blood sugar. Signs include:

• Headache

• Hunger

• Dizziness or weakness

• Fast heartbeat

• Feeling confused or irritable

• Feeling drowsy or sweaty

Your doctor or nurse should explain how to treat low blood sugar if it happens.

Digestive Symptoms

Mounjaro can affect your stomach and digestion. These side effects are common:

• Indigestion (dyspepsia)

• Stomach bloating

• Burping

• Excess wind (flatulence)

• Heartburn or acid reflux (also called GORD)

Changes in Appetite and Energy

• Reduced appetite – especially in those taking Mounjaro for type 2 diabetes

• Feeling tired or lacking energy (fatigue)

Other Common Side Effects

• Dizziness – more often in those using Mounjaro for weight loss or obesity

• Low blood pressure – also more common in weight management use

• Hair thinning or hair loss (seen in some people using Mounjaro for weight loss)

• Fast heartbeat (common with diabetes use, less common with weight management)

• Injection site reactions – such as redness, itching, or mild swelling

Changes in Blood Tests

Some people may notice changes in blood test results while using Mounjaro:

• Raised pancreatic enzymes (like amylase or lipase) – more common with diabetes treatment

• Higher levels of calcitonin – a hormone linked to thyroid function (more common in weight loss treatment)

• Gallstones – common in those using Mounjaro for weight management

If you notice any unexpected symptoms while using Mounjaro, speak to your GP, nurse, or pharmacist. Always read the patient information leaflet that comes with your medicine and report serious or unusual side effects to the MHRA Yellow Card Scheme.

Warnings & Precautions

Mounjaro usage also comes with a number of warnings and precautions that people should be aware of when they are using the medication. The warnings associated with Mounjaro include the risk of:

• Thyroid tumours

• Pancreatitis

• Hypoglycemia

• Severe allergic reactions

• Kidney failure

• Gallbladder problems

Blindness

Although blindness is not listed as a known side effect in the official patient leaflet, some people may notice blurred vision (Etminan et al, 2025). This is often linked to sudden changes in blood sugar levels.

There have been rare reports of a serious eye condition called Nonarteritic Anterior Ischaemic Optic Neuropathy (NAION), which can cause sudden and sometimes permanent vision loss. Some early studies have connected this condition to GLP-1 receptor agonists like Mounjaro.

While this side effect is uncommon, people with existing eye problems – such as diabetic retinopathy – may face a higher risk. If you experience any changes to your vision, speak to a healthcare professional straight away.

Regular eye check-ups are especially important if you have a history of diabetes-related eye conditions.

How long do mild side effects of Mounjaro last?

For people experiencing the mild side effects of Mounjaro, such as nausea or diarrhoea, it's common for these symptoms to be temporary and last for a few days or weeks. As your body gets used to the medication these mild side effects will diminish over time (Sutherby & Brewer, 2023).

How long do severe side effects of Mounjaro last?

Severe side effects of Mounjaro, such as severe digestive problems may last for longer periods of time than more common side effects. These side effects were not common during clinical trials of Mounjaro, however, they are possible. These side effects may last for an extended period and could lead to long-term treatment being required.

When should you see a doctor about Mounjaro side effects?

If you believe that you are experiencing side effects caused by Mounjaro it is important to seek medical attention, particularly if you experience severe side effects, or side effects that persist. The Medicines and Healthcare Products Regulatory Agency (MHRA) also recommends that you report any suspected side effects to their Yellow Card scheme which is used to help monitor the safety and effectiveness of medications in the UK. 

Is Mounjaro available to buy online?

If you are looking to purchase Mounjaro online and you live in the United Kingdom, look no further than UK Meds. At UK Meds, we offer Mounjaro as well as other weight loss medications such as Saxenda and Wegovy that you can purchase online. To purchase Mounjaro online from UK Meds you will need to complete our online consultation that, when approved, will allow you to purchase the medication using a free private prescription. This is necessary as Mounjaro is a prescription-only medication.

Essential Tips for Using Mounjaro Safely and Effectively

Want to get the best results from Mounjaro? UK Meds' complete guide to Using A Mounjaro Injection covers everything you need to know, from:

• Managing your dose

• Tracking progress

• Dietary changes

• Exercise recommendations

• Dealing with side effects

• Which vitamins you can take

• How to handle sulphur burps

• Where to find support in the UK

• Storage instructions & temperature advice

• Microdosing GLP-1 Medications for Weight Loss: Is It A Good Idea?

Our usage guide has all the advice you need to kickstart a smoother weight loss journey with Mounjaro.

Medically Reviewed by:
Dr. Alexis Missick MBChB. MRCGP
GMC reference no: 7151419
LinkedIn
Website

Sources

• PIL - Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen - EMC

• Mounjaro - How Mounjaro Works

• Within Health - Tirzepatide Mounjaro Weight Loss Risks