How tirzepatide works?

If you know anything about Mounjaro, it’s probably that it can drive impressive weight loss results. After taking it for over a year, you could lose up to 25% of your starting weight.

But do you know how it works? Basically, Mounjaro—which is the brand name for tirzepatide, its active ingredient—makes you feel full, so you eat less. Here’s the lowdown on how it does that.

What is tirzepatide?

Tirzepatide is a weight loss medicine that works by acting like two of the body’s natural appetite-suppressing hormones, glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP). Tirzepatide is also used to treat type 2 diabetes.

FYI: You might hear Mounjaro injections or tirzepatide being referred to as a GLP-1/GIP receptor agonist, which is another way of describing the above.

By bringing on the effects of these two hormones, tirzepatide suppresses your appetite and keeps cravings at bay. It does this in a few ways:

• Tirzepatide delays gastric emptying meaning food remains in your stomach longer, which keeps you feeling full.
• It regulates your appetite and reduces “food noise” so you’re not always thinking about your next meal.
• It improves blood sugar control.

Is tirzepatide effective for weight loss?

Yes—very. Let’s take a look at some tirzepatide weight loss results from scientific research. 

In one clinical trial, people taking tirzepatide for 72 weeks lost up to 22.5% of their starting weight. These results align with other research. Another trial that ran for 88 weeks showed a mean weight loss of 25.3%.

Heads up: These results are average figures taken from big groups of people. That means that some people lost more while others lost less.

There’s no way to predict how Mounjaro/tirzepatide will affect you personally—and if your numbers look different from the above, that’s absolutely fine. You’re on your own journey and you’ll reach your goals when you’re meant to.

How to take tirzepatide injections

You should inject tirzepatide into the fatty tissue just under your skin, either on your stomach, thigh, or the back of your upper arm, once per week.

It doesn’t matter which area you pick (and you can use the same area of your body from week to week), but you should inject into a different spot each time.

Using tirzepatide injector pens is pretty straightforward, but there are a few steps you’ll need to follow. We’ve covered them in detail here.

You’ll start on the lowest dose of tirzepatide. This allows your body to get used to the medicine, so that you can handle higher strengths later on. It also reduces your risk of getting side effects.

If you’re tolerating the medicine okay, your provider will increase your dose every four weeks, until you reach your maintenance dose. This is the strength of the medicine where it has the effect we want it to without causing any nasty side effects. Your provider will confirm which dose that is for you personally.

Common side effects of tirzepatide

Yep, tirzepatide injections can have side effects. But the good news is that these are usually mild and go away on their own. 

Still, it’s helpful to know what you might expect when taking it. Because of tirzepatide’s effect on the stomach—one way it makes you feel full is by slowing your digestion—its most common side effects are gut-related.

These Mounjaro side effects might affect over one in ten people:

• Nausea
• Vomiting
• Diarrhoea
• Stomach pain
• Constipation

And up to one in ten may experience these:

• Dizziness
• Indigestion
• Bloating, burping or gas
• Heartburn
• Fatigue

These symptoms are similar to Saxenda and Wegovy side effects, since these medicines both also work to slow your digestion.

What about long-term side effects of tirzepatide? It’s rare, but some people can develop pancreatitis (inflammation of the pancreas) or gallbladder disease. These conditions are treatable and are estimated to affect less than 1% of people on Mounjaro.

If you have a severe pain in your back or stomach that doesn’t go away, or any other symptoms that are getting worse and not clearing, speak with your doctor.

Side effects support at Voy

"If you're using Voy and you experience any side effects, rest assured that our expert clinicians are just a message or phone call away. They can adjust your dose, prescribe medication to ease your symptoms, or simply offer reassurance.

Everyone responds differently to weight loss treatment and we'll help you find what feels right for you."

Phoebe Fox - Weight Loss Specialist

Tirzepatide vs other weight loss medications

How do tirzepatide injections compare to other weight loss medicines out there? Glad you asked—read on to find out. 

How they work

All of the weight loss injections that are currently available (Saxenda, Wegovy and Mounjaro) work by mimicking the behaviour of our natural hormones.

However, both Saxenda (liraglutide) and Wegovy (semaglutide) only act like GLP-1, whereas Mounjaro (tirzepatide) brings on the effects of GLP-1 and GIP.

There’s also orlistat weight loss capsules, which are the only tablets approved for weight loss in the UK. They work by reducing the amount of fat you absorb from your food. Orlistat isn’t an appetite suppressant like GLP-1 medications.

If you’re interested in how a potential GLP-1 pill might compare with tirzepatide, see our guide on orforglipron vs tirzepatide.

Efficacy

Tirzepatide’s dual action is what makes it so potent. Per clinical research:

• People lost 7.4% of their starting weight after taking Saxenda (liraglutide) for a year
• Those on Wegovy (semaglutide) lost 14.9% after 68 weeks (with a higher dose of 7.2mg leading to a 20.7% weight loss after 72 weeks, making the gap in effectiveness between Wegovy and Mounjaro narrower than ever.)
• Taking Mounjaro (tirzapatide) for 88 weeks led to a mean 25.3% drop in weight

Dosing

Each of these medicines is available in different doses.

With weight loss injections, you start on the lowest strength and gradually move up (your provider will only dial up your dose if you’re tolerating the medicine) to your maintenance dose. For Saxenda, which is taken daily, your dose can be increased every week. Wegovy and Mounjaro are taken weekly and your dose can go up every four weeks.

Side effects

We mentioned earlier that the side effects of tirzepatide are similar to those of Wegovy and Mounjaro. Here’s a closer look at how they stack up.

May affect over one in ten people

Mounjaro

Wegovy

Saxenda

Orlistat

Nausea

Vomiting

Diarrhoea

Constipation

Stomach pain

Headache

Increased need to pass stools

Wind

Oily discharge, Fatty or liquid stools

Weakness or tiredness

Is tirzepatide right for you?

Ready to take the next step in your weight loss journey? We’re right here with you—and we know you can reach your goals.

Through our weight loss treatment, you’ll get monthly weight loss medication posted to you plus clinical support from your dedicated team of treatment specialists and clinicians. We’ll help you transform your lifestyle via our structured habit-change approach.

Our Voy weight loss results can give you an idea of what to expect: most people lose 10-15% body weight with us and 97% said they feel more confident. Not to mention that we’re the highest-rated weight loss provider on TrustPilot and the App Store.

We can also advise on which medication is best for you, whether that’s Mounjaro weight loss injections or something else.

Take our quiz to see if you’re eligible for the treatment. Our clinicians will review your answers and come back to you asap.