Mounjaro® Injectable Pen

Mounjaro and Wegovy are two different injectable weight loss medications with differing mechanisms of action.

Wegovy contains the active ingredient semaglutide, which mimics a hormone called GLP-1 to help regulate appetite and slow down stomach emptying.

Wegovy also improves insulin sensitivity, stabilising blood glucose levels and preventing sudden spikes and crashes to prevent excessive hunger signalling by the brain.

Mounjaro contains a different active ingredient, tirzepatide, which also mimics GLP-1, in addition to mimicking another hormone known as GIP to further enhance insulin release by the body.

Recommended reading: Wegovy vs Mounjaro: Weight Loss Injection Comparison

Mounjaro is not the same as Ozempic. While both medications are prescribed for weight loss, they have different active ingredients and mechanisms of action.

Mounjaro contains tirzepatide, an active ingredient that mimics the gastric inhibitory polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) hormones. In contrast, Ozempic contains semaglutide, an active ingredient that mimics the GLP-1 hormone, but not the GIP hormone.

Yes, you can switch from Mounjaro to Wegovy. It is recommended to leave at least 2 weeks after your final Mounjaro injection before starting Wegovy treatment. This ‘wash-out’ period lets Mounjaro’s active ingredient fully clear from your body and reduces the likelihood of unwanted interactions between Mounjaro and Wegovy.

When you begin Wegovy treatment, you will be prescribed the starting dose of 0.25mg, even if you were previously taking higher strengths of Mounjaro. This step is needed to reduce the risk of side effects and also allows your body to adjust to Wegovy’s active ingredient (semaglutide).

Thinking about switching from Mounjaro to Wegovy? Our customer service team is here to help. Our clinical team will also review your treatment to ensure Wegovy is safe and appropriate for you.

Orlistat is a clinically proven oral weight loss treatment that reduces total calorie intake by limiting the absorption of dietary fat.

In contrast, Mounjaro is a weight loss injection that works differently by stabilising blood sugar levels to reduce appetite and slowing stomach emptying, helping you feel fuller for longer.

Mounjaro and Zepbound are both medications containing the active ingredient tirzepatide, which mimics hormones to make the body feel fuller and reduce appetite.

Zepbound is the US name for the same weight loss medication, whereas in the UK, tirzepatide is licensed under the name Mounjaro.

The medications function in the same way and are both prescribed for weight loss and metabolic regulation.

Mounjaro can reduce the effectiveness of oral contraceptive pills, particularly during the first four weeks of treatment and after each dose increase. This is due to the fact that the active ingredient in Mounjaro, tirzepatide, slows gastric emptying, which can affect the absorption of the pill and reduce its effectiveness in preventing unplanned pregnancy.

Therefore, if you are using oral contraception (i.e. the combined pill or the progestogen-only pill) and taking Mounjaro, it is important to use an additional barrier method of contraception (e.g. condoms) alongside oral contraceptive pills for 4 weeks after starting the medication and for 4 weeks after any increase in the Mounjaro dose. You should also consider switching to long-acting contraceptives (e.g. an IUD) while taking Mounjaro.

Furthermore, diarrhoea and vomiting are common side effects of Mounjaro that can reduce the effectiveness of oral contraceptives. If vomiting occurs within three hours of taking the contraceptive pill, or if you experience severe diarrhoea for more than 24 hours, you should follow the missed pill rules as instructed in the patient information leaflet of your oral contraception. You should also consider an alternative non-oral method of contraception (e.g. an IUD or condoms) if your diarrhoea or vomiting persists.

Mounjaro can result in a loss of body fat, which may affect menstrual cycles in some women. This is due to the fact that menstrual cycles are affected by levels of the hormone oestrogen, which is produced by fatty tissues in the body.

Women who experience changes in menstrual cycles from taking Mounjaro are recommended to consult a doctor for further advice.

It is not advisable to take Mounjaro (tirzepatide) during pregnancy, as there is limited data on its safety and impact on developing children.

If you are pregnant or intend to become pregnant and have taken Mounjaro, discuss your usage of this medication with your doctor immediately.

You can buy Mounjaro online in the UK with a prescription from a fully registered and trusted online pharmacy such as Pharmica. Our licensed prescribers and pharmacists can offer clinically proven prescription weight loss treatment, along with personalised advice on diet and exercise, as part of our comprehensive weight management service. We’re proud to be rated the UK’s #1 weight loss service on Trustpilot, having helped thousands of patients successfully achieve their weight loss goals.

To order Mounjaro from Pharmica, simply complete our short medical questionnaire. This will be reviewed by our clinical team to ensure the treatment is safe and appropriate for you. Following approval, your medication will be discreetly delivered to you along with your Pharmica welcome pack.

Should you require any help or support while using Mounjaro, our dedicated customer service team is available to assist you.

Before use, Mounjaro should be stored in the fridge between 2°C and 8°C. Keep the pen in its original packaging until ready for use. Do not freeze it.

Once you have used your Mounjaro pen for the first time, it can be stored at room temperature (not exceeding 30°C) for up to 30 days, or kept in the fridge until your next dose. When not in use, always keep the pen cap on to protect it from light, as exposure may reduce the effectiveness of the medication.

No, Mounjaro is a prescription-only medication in the UK, which means it can only be supplied following assessment by a qualified healthcare professional.

At Pharmica, you can buy Mounjaro following the completion of a short online medical questionnaire to determine your eligibility. Once reviewed and approved, your medication will be delivered straight to your door, along with your Pharmica Welcome Pack.

If you have any questions about Mounjaro, our clinical team is here to provide expert advice throughout your treatment. Our friendly customer service team is always ready to offer clear, practical guidance to help you get the best weight loss results.

• Tirzepatide once weekly for the treatment of obesity, 2022. [Accessed 4th July 2025]
• Electronic medicines compendium: Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen. [Accessed 4th July 2025]
• Eli Lilly & Company: Mounjaro Patient Booklet, 2025. [Accessed 4th July 2025]