Can Mounjaro Make You Tired?

Mounjaro (tirzepatide) is one of the most effective weight-loss treatments currently available, but one question I’m frequently asked as a prescribing pharmacist is:

“Can Mounjaro make you tired?”

The honest answer is yes, it can — but in most cases, not for the reason people assume.

Drawing on my experience prescribing and reviewing Mounjaro for a large number of patients, I want to explain when tiredness can occur, why it happens, and what actually helps in real-world practice.

How Common Is Tiredness when using Mounjaro?

In my clinical experience, around 20% of patients report feeling unusually tired at some stage while taking Mounjaro.

That means many patients do not experience fatigue at all. When tiredness does occur, it is usually mild, temporary, and reversible.

When Does Fatigue Usually Appear?

Tiredness is uncommon in the first week of treatment.

Most patients who report fatigue do so:

• Around month 2 onwards
• Often after significant early weight loss
• Occasionally following a dose increase

On rare occasions, I have seen patients experience tiredness early on, but this is not the typical pattern.

Is Mounjaro Actually the Cause?

In around 80% of cases, fatigue is not caused directly by Mounjaro itself.

Instead, it’s usually due to:

• A large calorie deficit
• Dehydration
• Poor protein intake
• Electrolyte imbalance, particularly low sodium
• Avoiding carbohydrates altogether

Mounjaro significantly suppresses appetite. Without proper guidance, many patients unintentionally under-fuel their bodies — and fatigue is one of the first signs.

Who Is More Likely to Feel Tired?

Both men and women can experience tiredness.

One consistent pattern I see is in patients who:

• Have sedentary lifestyles
• Work jobs which require being seated for long periods of time
• Are not consciously managing hydration, salt, or nutrition

This isn’t about lack of effort or “doing it wrong” — it’s usually about not realising how little the body is actually getting.

A Real-World Case Example

One male patient with a demanding office job achieved excellent early weight-loss results on Mounjaro.

However, around week 7, he began feeling exhausted throughout the day.

On reviewing his routine, we identified:

• Very low carbohydrate intake
• A significant calorie deficit
• Inadequate hydration

Our advice was simple and practical:

• Increase calories slightly
• Increase carbohydrates and protein intake
• Increase daily water intake
• Add electrolytes once or twice per week

Within 7 days, his energy levels improved dramatically — without slowing his weight loss.

The Most Common Preventable Causes of Fatigue

Based on our experience at TrustMeds, the most common preventable causes are:

• Eating too little
• Skipping meals
• Avoiding salt
• Cutting out carbohydrates completely
• Not drinking enough fluids

None of these are required for safe or effective weight loss.

What Actually Helps in Practice?

This is the guidance I routinely give patients — and what genuinely works:

• Increase water intake consistently
• Do not eliminate carbohydrates such as bread and pasta — they support energy and metabolic function
• Eat small, regular, protein-rich meals
• Maintain adequate fibre intake
• Avoid extreme restriction
• Consider electrolytes, particularly if energy feels flat or you feel light-headed

Sustainable weight loss should feel manageable, not exhausting.

When Should Tiredness Be Taken Seriously?

Fatigue should be reviewed if it:

• Persists despite improving nutrition and hydration
• Worsens over time
• Interferes with daily functioning

At that point, I advise patients to speak to our pharmacists or prescribing team. We will review:

• Dose and escalation plan
• BMI and rate of weight loss
• Diet quality
• Other side effects

Often, small adjustments are all that’s needed.

How Does Mounjaro Compare to Other Weight-Loss Injections?

In my experience, Mounjaro tends to cause less fatigue than Wegovy.

It also generally has a better gastrointestinal side-effect profile, which helps patients maintain consistent nutrition — an important factor for energy levels.

A Common Misconception

Many patients assume their experience will mirror:

• A friend’s journey
• Or something they’ve read online

In reality, everyone responds differently. This is why choosing a service that provides personalised clinical support matters. We treat each patient as an individual and provide ongoing, unlimited support, not just a prescription.

Final Thoughts

Mounjaro can be a highly effective and life-changing treatment. If tiredness occurs, it’s usually a sign that the body needs:

• Better hydration
• Better nutrition
• Better support

It does not usually mean the medication isn’t right for you.

With the right guidance, most patients regain their energy quickly — and continue to lose weight safely and sustainably. Ready to start your weight loss journey with TrustMeds?

Read more here if you want to find out if Mounjaro can cause hair loss.