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Tips for starting Mounjaro: what you need to know before treatment

Simon Edward • 14 March 2025

Are you using Mounjaro weight loss injections for the first time? Discover helpful tips for starting Mounjaro.

Are you about to begin your personal weight loss journey with Mounjaro? Perhaps you're considering it?

We wish you the best of success. Losing weight can have life-changing effects on your health, energy levels and overall well-being.

That said, it won't be a walk in the park. While the injections can be a huge help, losing weight with Mounjaro is also about developing healthy eating habits, exercising more and improving your sleep routine. You might also experience unpleasant side effects – especially when you first start out or switch to a higher dose.

We want your journey with Mounjaro to be as smooth, enjoyable and effective as possible. That's why we've put together these helpful tips for starting Mounjaro. Keep these tips in mind and those first few weeks should be a little easier.

Managing your weight loss expectations

Mounjaro is one of the most effective weight loss medications currently available. In a clinical trial, Mounjaro users lost an average of 21% of their starting weight over 72 weeks of treatment.¹ These users also followed a calorie-controlled diet and started exercising more regularly.

But keep in mind that this was a long-term study. You shouldn't expect instant results with Mounjaro. As with many medications, your body needs time to adjust to Mounjaro before you start seeing results.

Don't expect to lose more than a few pounds during the first four weeks. By the end of month three, however, your body should have adjusted to a higher dose and your efforts should be paying off. You should expect to have lost around 10% of your starting weight by this point.

Your weight loss should gain momentum from here. Expect to have lost around 15% by the end of month five. From month six onwards, depending on your tolerance and side effects, you may be on the maximum dose. If so, you can expect to have achieved weight loss of around 21%.

Read our guide to weekly weight loss on Mounjaro to learn more.

Knowing the potential side effects

Think of your first month on Mounjaro as a dry run. It's about learning how to work with the medication and allowing your digestive system to adjust to its effects.

All medications can produce side effects. These are unexpected (and sometimes unpleasant) effects that happen alongside the drug's intended effect.

Picture representing stomach pain, and discomfort.

Because Mounjaro's affects the hormones that control digestion, you're most likely to feel side effects in your stomach. Among the most common are nausea, bloating, acid reflux, vomiting and diarrhoea.

Keep in mind that not everyone is affected in the same way. Some people feel side effects more strongly than others. If you're lucky, you might not experience any side effects at all – or experience just one or two mild side effects.

Side effects are most likely to happen when you first start taking Mounjaro or switch to a higher dose. They often become less pronounced as your body gets used to the new dose.

Read our guide to Mounjaro side effects to learn more and get useful tips on managing some of the most common effects. Please refer to the manufacturer's website for a complete, up-to-date list of potential side effects.

Establishing a good routine

You need to choose a day to take Mounjaro and then take it once a week on the same day, injecting it into a different area of skin each time.

People who work during the week often find it's best to take it at the beginning of the weekend. This way, any side effects will likely have become less pronounced by the time they start work on Monday.

It doesn't matter what time of day you take the medication. Nor does it matter how recently you've eaten.

However, it can be difficult to establish a new routine. For this reason, choosing a time and sticking to it is often helpful. As you continue treatment, taking your injection should start feeling as natural as brushing your teeth in the morning.

Read our guide on when to take Mounjaro to learn more.

Injecting your Mounjaro pen for the first time

Mounjaro is supplied in a KwikPen. This device makes it easy to inject yourself with the drug. It's a similar size to a permanent marker pen and has a tiny needle that penetrates just below the skin.

If you join the SemaPen programme, you'll automatically receive a new pen every four weeks. Each contains enough liquid for four doses and a little extra for priming. Priming is when you squirt some liquid before each use to make sure the medication flows all the way to the end of the needle.

It only takes a couple of minutes to administer your dose. However, you should always wash your hands beforehand and have an alcohol wipe (or soap and water) ready to clean the injection site.

Ideal sites are the front of your thighs and the soft part of your belly (make sure you stay at least 5cm away from your belly button). Choose a different area of skin each time.

Your needles are supplied in a separate pack. Each dose requires a new sterile needle. The needles come as screw-on caps with a plastic sheath covering the needle. Peel off the paper seal and screw it onto the end of the pen.
You now need to prime the pen. Click the dial until you see an extended line in the dose window. Hold the pen upright, remove the plastic sheath from over the needle and press down on the dose knob. This will squirt a small amount of liquid from the needle.
Now, you can prepare your dose. Twist the dial until it clicks. You'll see the dose number in the viewing window.
Swab the end of the needle and the injection site. Pinch a handful of skin between your thumb and forefinger and push the needle in just under the skin.
Press the dosing knob in as far as it will go. Count to 10 and then release.
Dispose of your needle in the sharps box provided and put the pen cap back onto the end of your pen.

When you first begin, it's usual to feel a little nervous. However, most people quickly get used to it and are surprised at how easy it is.

We hope these tips help you start your Mounjaro weight loss journey on the right foot. Need a little more support? When you join the SemaPen programme, you can access helpful guides and proactive, tailored support from real obesity experts. It's easy to find out if you're eligible – simply complete our online consultation and we'll recommend the best treatment pathway for you.

Sources

1. Jastreboff, A.M. et al. (2022) "Tirzepatide Once Weekly for the Treatment of Obesity" New England Journal of Medicine, 387(3) https://doi.org/10.1056/NEJMoa2206038

This article was reviewed by and approved by Alice Fletcher, Bariatric Dietitian, on 5 March 2025.

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