While most side effects are mild and temporary, doctors are warning some serious reactions can occur, though they are rare, particularly pancreatitis, a potentially severe inflammation of the pancreas.

It’s vital to be aware of symptoms that require urgent medical attention:

  • Severe or ongoing stomach pain that may spread to your back and are not improving (possibly indicating pancreatitis)
  • Persistent nausea or vomiting
  • Yellowing of skin or eyes (could signal liver or gallbladder issues)
  • Signs of infection, fever, or unusual weakness
  • Difficulty breathing, wheezing or swelling in face or throat (signs of an allergic reaction)

If you experience these, stop your medication immediately and seek emergency medical help by going to Accident and Emergency (A&E) or call 999 immediately.

Dr Babak Ashrafi from ZAVA explains: “Weight loss injections like Mounjaro and Wegovy are one of the most exciting developments we’ve seen in obesity treatment in recent years.

“These medications don’t just help reduce weight, they tackle one of the root causes by regulating appetite, which can be life-changing for people who’ve struggled with traditional weight loss methods. Clinical evidence shows that they can lead to significant, sustained weight loss and improvements in overall health, including blood pressure and cholesterol.

“But they’re not a magic fix. Long-term success comes from combining these treatments with healthy eating, regular physical activity, and the right support. That’s why it’s so important to use these injections under the guidance of a healthcare professional, who can monitor your progress and make sure they’re safe and suitable for your individual needs.”

The Mounjaro weight-loss jab is officially being introduced on the NHS, but only for a limited group of patients with a BMI over 35 and a related health condition.

Despite growing excitement, the treatment isn’t as easily accessible as some may think.

Still, interest is soaring.

In the UK, Google searches for Mounjaro have jumped by more than 5,000%, with people asking questions like “Criteria for Mounjaro on NHS” and “Does Mounjaro work for everyone?” as they explore their options.

More Mounjaro news…

How does Mounjaro work for weight loss?

Week 1 – Adjustment phase

Starting weight loss injections triggers your body to adapt to the new medication, explains Dr Ashrafi. Because these treatments mimic the naturally occurring GLP-1 hormone, they influence your appetite and digestion, which can initially cause side effects such as:

  • Nausea or vomiting
  • Mild digestive discomfort
  • Fatigue or headaches

These symptoms usually appear in the first few days as your system adjusts. To ease discomfort, it’s recommended to eat smaller, low-fat meals and avoid greasy or rich foods. Staying hydrated and resting are also important during this period. While you might experience signs of discomfort, it’s important to take your medication exactly as prescribed by your doctor and listen to your body. 

Week 2: Side effects may peak

For many, side effects can continue during the second week, as the body continues to respond to the medication. Nausea, headaches, or digestive upset often begin to decrease as treatment continues.

If side effects do not improve, healthcare providers may adjust the dosage or suggest a slower increase to help your body acclimate more comfortably. Staying well-hydrated and resting when needed are simple ways to ease symptoms.

Week 3: Settling into a routine

By the third week, most patients report fewer side effects as their bodies adjust. At this stage, some patients begin noticing early positive changes, such as reduced appetite, feeling fuller sooner during meals or slowing gastric emptying. Remember, these injections work by mimicking the GLP-1 hormone, which regulates hunger and digestion.

It is crucial to maintain a balanced diet and regular exercise to support your weight loss journey and overall health.

Week 4: Visible changes emerge

At the 4 week mark many people start seeing early changes in weight and energy levels.

Clinical trials show that with continuous use combined with lifestyle modifications, Wegovy users lost up to 15% of their body weight over 68 weeks, while Mounjaro users experienced at least 22.5% reduction over 72 weeks.

Weight loss injections have also been shown to improve markers like blood pressure, cholesterol, and blood sugar control, important benefits for long-term health.