Mounjaro ingredients: What they do and why they matter

Ever wonder what exactly is going into your body every time you inject Mounjaro? Each dose isn’t just a single ingredient—it's a precise formula designed for safety and effectiveness.

From stabilisers to buffers and preservatives, each component has a purpose, and without them, the medication wouldn't quite be the same.

Read as we break down each ingredient in Mounjaro and what role it plays, plus what you can expect when the medication is in action.

What are the ingredients in Mounjaro, and what do they do?

In a nutshell, Mounjaro has one main ingredient doing the heavy lifting, supported by several others that help keep it stable, sterile, and as comfortable to inject as possible [2].

Tirzepatide

Tirzepatide is the active ingredient in Mounjaro, the one that delivers therapeutic benefits [1].

We'll explain how tirzepatide works shortly, but it basically is the star of the show. It helps keep blood sugar levels in check, reduces appetite, and contributes to weight loss.

Sodium chloride

Sodium chloride is a type of salt that works as a tonicity adjuster, making the injection isotonic to your body's natural fluids [3].

In plain English, it ensures the medication has a similar salt concentration to your blood and tissues, which can prevent stinging and irritation during injection.

It also helps tirzepatide stay intact and do its job effectively, extending its shelf life.

Sodium phosphate dibasic heptahydrate

Another type of salt, sodium phosphate dibasic heptahydrate, acts as a buffer to maintain Mounjaro's pH and make the injection less irritating to the skin tissue [4].

Like sodium chloride, it prevents tirzepatide from degrading and helps maintain its potency over time.

Hydrochloric acid and sodium hydroxide

These two work as a balancing act to fine-tune Mounjaro's pH. Hydrochloric acid lowers the pH if the solution is too basic, while sodium hydroxide nudges it back up if the solution is too acidic, keeping the formulation within the optimal pH range.

Glycerol

Glycerol is a type of alcohol, and in Mounjaro, it acts as a stabiliser. It prevents chemical reactions from occurring while also keeping the medication at the right fluid balance and viscosity, preventing it from sticking to the walls of the Mounjaro pen.

Benzyl alcohol

Like the name suggests, benzyl alcohol is also a type of alcohol, used in injectable medications as a preservative. It prevents bacteria from growing in the solution (helping it last longer) and keeps the injection sterile and safe for use.

Phenol

Phenol is both a preservative and a stabiliser in Mounjaro. It protects against contamination and helps keep the medication potent.

And a nice extra: it slightly numbs the injection site (typically the stomach, thigh, or upper arm), making each dose a tiny bit easier to administer.

Water for injection

Water for injection (WFI) is the base of the entire formulation. It's what everything else is dissolved or dispersed in, and what carries tirzepatide through the injection.

As you can imagine, this isn't your usual distilled or bottled water. It’s pharmaceutical-grade, sterile, and free from contaminants that could otherwise irritate your skin or damage the medication [5].

How tirzepatide works in the body

Mounjaro's active ingredient deserves its own spotlight. So, what exactly does tirzepatide do in your body?

Well, tirzepatide is a dual GLP-1 and GIP receptor agonist. In other words, it mimics the effects of both glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) in your body, two naturally occurring hormones that influence blood sugar, appetite, and digestion [1].

By doing so, tirzepatide signals the pancreas to release insulin only when glucose is present, and alerts the liver to lower glucose production, so blood sugar doesn’t spike unnecessarily.

The result? Your digestion slows down, helping you feel fuller for longer, and you're less likely to experience cravings in between meals. It becomes easier to stick to a calorie deficit, which ultimately supports weight loss and management.

Tirzepatide also aids blood sugar control, keeping levels stable throughout the day, improving glycemic control, and reducing your risk of complications linked to type 2 diabetes.

What can I expect when taking tirzepatide?

We just touched on the main benefits of taking Mounjaro (or tirzepatide): slower digestion, reduced hunger levels, more stable blood sugar, and weight loss.

But you'll likely go through a few other changes and reactions, especially during the first few weeks of treatment and during dosage escalations. Like any other medication, Mounjaro comes with potential side effects [6].

Luckily, most are mild and tend to improve over time:

• Nausea
• Diarrhoea
• Vomiting
• Constipation
• Indigestion
• Abdominal pain
• Acid reflux and heartburn
• Bloating and gas
• Fatigue
• Headaches

Some patients have reported experiencing skin sensitivity, dry mouth and bad breath, hair loss, eggy burps, and body aches, though these are less-discussed side effects.

There are also some serious side effects which, although rare, are worth knowing. These include allergic reactions, hypoglycemia, and pancreatitis (with symptoms like sudden, severe abdominal pain, fever, and in some cases, persistent vomiting).

If you believe something serious is going on, that's your cue to stop Mounjaro and seek medical attention ASAP.

What strengths does Mounjaro come in?

Mounjaro is available in a range of strengths:

• 2.5mg/0.5mL
• 5mg/0.5mL
• 7.5mg/0.5mL
• 10mg/0.5mL
• 12.5mg/0.5mL
• 15mg/0.5mL

Mounjaro is usually supplied as a one-dose injection pen or a 4-dose pen known as Mounjaro Kwikpen.

Your healthcare provider will recommend the right dose for you based on several factors, including your body mass index and medical history, particularly any underlying obesity-related conditions like hypertension or heart problems.

They'll also take into account any other medications you're on. For example, if you take other diabetes medicines, they'll likely adjust your dose to prevent low blood sugar.

How does dosing usually progress?

The starting Mounjaro dose is 2.5 mg. From there, you typically have the option to increase your dose every 4 weeks in 2.5 mg increments until you hit the maximum of 15mg [6].

However, your escalation schedule may vary depending on how your body reacts to the medication.

For example, if you're struggling with side effects like nausea or vomiting, your doctor may give your body more time to adjust—say 6 weeks instead of 4—before moving to the next dose.

Mounjaro vs Wegovy

Mounjaro and Wegovy are both once-weekly injections that control blood sugar and reduce appetite, but they're not exactly the same. Let's look at them side by side:

Active ingredient comparison

We know that Mounjaro has an active ingredient called tirzepatide, which targets two hormonal receptors (GLP-1 and GIP) to support weight loss and treat diabetes.

Wegovy, on the other hand, contains semaglutide (the same active ingredient used in Ozempic). Semaglutide activates only the GLP-1 receptor, but still helps to control blood sugar, slow digestion, and curb hunger.

This raises a common question: which one is more effective, Wegovy or Mounjaro?

In clinical trials, patients on the highest dose of Wegovy lost up to 20.7% of their body weight, compared to 20.9% with Mounjaro at its highest dose [7]. This shows that both can be highly effective when used consistently and alongside diet changes and regular exercise.

Dosing differences

With Mounjaro, you start on 2.5 mg once weekly and, depending on how your body reacts, your doctor increases the dose by 2.5 mg every 4 weeks.

Wegovy's escalation schedule is different. The starting dose is typically 0.25 mg once a week and, if your body responds well, it increases gradually every 4 weeks until you reach the maintenance dosage of 2.4 mg once per week.

Switching from Mounjaro to Wegovy

As of 1 September 2025, Eli Lilly, the manufacturer of Mounjaro (tirzepatide), increased its UK list price to align with other developed countries. This nationwide change applies to providers including pharmacies, private clinics, and digital platforms.

In response, we’ve lowered the price of our Wegovy programme by 25%, and we’re making it easier for patients to switch without starting over, so that effective treatment remains within reach for as many people as possible.

So, if you've been wondering if you can switch from Mounjaro to Wegovy, the good news is that it's both safe and straightforward.

When making the switch, Juniper patients don’t need to restart at the lowest dose. If clinically appropriate, they can continue at a higher dose aligned with recent treatment history. We also only require a 7-day gap between your last Mounjaro dose and your first Wegovy dose — unlike most providers, who require 28 days.

At Juniper, we make that switch seamless and fully supported — so you can protect your progress without paying more than you need to. Our clinical switching protocol is simple and safe:

• Review — Your clinician assesses your treatment history and dose tolerance.
• Match — If eligible, you start on an equivalent high dose to avoid losing progress.
• Transition — Only a 7-day window is required between your last Mounjaro dose and your first Wegovy dose (most providers require 28 days).
• Support — Pharmacist check-ins, dose adjustments, and lifestyle guidance keep you on track.

Start your Wegovy switch today →

Find the right weight loss treatment with Juniper

Mounjaro might be the right solution for some, and Wegovy for others. At Juniper, we offer both options, so all our patients can access the weight loss medication that will best suit their body, initial weight, and lifestyle.

The Juniper Programme combines weight loss medication with dietitian-led health coaching and tracking, so you can lose weight and reach your goals for good.

Kickstart your weight loss journey with Wegovy or Mounjaro, two groundbreaking weight loss medications that mimic the GLP-1 and GIP hormones, respectively, to help control cravings, delay stomach emptying, and keep you feeling fuller for longer. These clinically backed treatments help members experience up to 23% body weight loss.

Plus, we have a team of expert dietitians and health coaches you can consult with to help you work through any challenges you're experiencing during your weight management journey. This approach sets you up for sustained weight loss, rather than a quick-fix solution.

This means you can continue to enjoy the things you love in moderation without ever feeling deprived.

Ready to see if Juniper is right for you? You can check your eligibility here.

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