By the third week on Mounjaro (tirzepatide), most patients continue their initial 2.5 mg weekly dose as their body adapts to this dual GIP and GLP-1 receptor agonist. Licensed in the UK exclusively for type 2 diabetes mellitus, Mounjaro works by enhancing insulin secretion, suppressing glucagon release, and slowing gastric emptying. During week three, gastrointestinal side effects often begin to stabilise, whilst blood glucose control continues to improve. This transitional period allows patients to become more familiar with injection technique and recognise how the medication affects appetite and glucose levels. Regular monitoring remains essential, particularly if you take other diabetes medications alongside Mounjaro.

What to Expect in Your Third Week on Mounjaro

By the third week of Mounjaro (tirzepatide) treatment, most patients are continuing their initial 2.5 mg weekly dose, which typically lasts for four weeks before any dose increase is considered. Mounjaro is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for the treatment of type 2 diabetes mellitus only. It is not approved for type 1 diabetes or diabetic ketoacidosis.

The medication works by enhancing insulin secretion when blood glucose levels are elevated, suppressing glucagon release, and slowing gastric emptying.

During week three, your body continues adapting to the medication's effects on glucose metabolism and appetite regulation. Many patients report that gastrointestinal side effects, which may have been prominent in the first two weeks, begin to stabilise or gradually improve. However, individual responses vary considerably, and some people may still experience notable symptoms as their system adjusts to the pharmacological changes.

Key expectations during week three include:

• Continued appetite suppression, often with reduced food cravings

• Ongoing adjustment of blood glucose levels

• Potential persistence or gradual improvement of gastrointestinal symptoms

• Increased familiarity with injection technique and timing

It is important to maintain regular blood glucose monitoring as advised by your diabetes care team, particularly if you are taking other glucose-lowering medications. The third week represents a transitional period where early treatment effects become more established, but full therapeutic benefits typically require several weeks to months of continued treatment.

If you experience severe or persistent abdominal pain (especially if radiating to the back) with or without vomiting, stop taking Mounjaro and seek urgent medical attention, as this could indicate pancreatitis. For women using oral contraceptives, be aware that Mounjaro may reduce their effectiveness; use additional barrier contraception for 4 weeks after starting treatment and for 4 weeks after each dose increase.

Common Side Effects During Week 3 of Mounjaro Treatment

Gastrointestinal side effects remain the most frequently reported adverse reactions during the third week of Mounjaro treatment. These occur because tirzepatide slows gastric emptying and affects gut motility as part of its mechanism of action. Common side effects at this stage include:

• Nausea – often most pronounced after meals, particularly large or fatty meals

• Vomiting – may occur in some patients

• Diarrhoea – may occur intermittently or persistently

• Constipation – affecting some patients, sometimes alternating with looser stools

• Reduced appetite – a therapeutic effect that can feel uncomfortable initially

• Abdominal discomfort or bloating

• Dyspepsia (indigestion)

Most patients find that gastrointestinal symptoms are most intense during the first two weeks and begin to improve by week three, though this timeline varies. The severity of side effects does not predict treatment efficacy, and some individuals tolerate Mounjaro very well from the outset.

To manage these effects, consider eating smaller, more frequent meals rather than large portions, avoiding high-fat or heavily spiced foods, and staying well hydrated. Eating slowly and stopping when comfortably satisfied rather than full can reduce nausea and discomfort. For constipation, increasing dietary fibre and fluid intake may help.

When to seek medical advice:

• Urgent medical attention is required if you experience severe, persistent abdominal pain (especially if radiating to the back) with or without vomiting – stop taking Mounjaro as this could indicate pancreatitis

• Contact your healthcare team if you have signs of gallbladder problems (right upper abdominal pain, fever, yellowing of skin/eyes)

• Seek medical advice if you have severe or persistent vomiting that prevents adequate fluid intake, or signs of dehydration (dark urine, dizziness, reduced urination) which could affect kidney function

• Report any visual changes, especially if you have pre-existing diabetic retinopathy

• Get immediate medical help if you experience signs of a severe allergic reaction (rash, swelling, difficulty breathing)

You can report any suspected side effects to the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or via the Yellow Card app.

Weight Loss and Blood Sugar Changes in the Third Week

By the third week of Mounjaro treatment, many patients begin to notice measurable changes in both body weight and glycaemic control, though the magnitude varies considerably between individuals. Clinical trials have demonstrated that tirzepatide produces progressive improvements in HbA1c and body weight over time, with effects becoming more pronounced as treatment continues beyond the initial weeks.

Regarding blood glucose changes, patients often observe more stable readings with fewer post-meal spikes during week three. Mounjaro's dual mechanism enhances glucose-dependent insulin secretion and suppresses inappropriate glucagon release, leading to improved glycaemic control without significantly increasing hypoglycaemia risk when used as monotherapy. However, if you are taking Mounjaro alongside other glucose-lowering medications—particularly insulin or sulphonylureas—your diabetes team may have adjusted these doses to prevent low blood sugar episodes.

Continue monitoring as advised and be aware of hypoglycaemia symptoms (trembling, sweating, confusion, palpitations). If your blood glucose falls below 4.0 mmol/L or you experience symptoms, take 15-20g of fast-acting carbohydrate (such as glucose tablets, fruit juice or sugary drink), wait 15 minutes, then recheck your levels. Contact your diabetes team if you experience recurrent hypoglycaemia, as your other diabetes medication doses may need adjustment.

Concerning weight loss, some patients notice modest weight reductions during the first three weeks, though individual responses vary significantly. Weight loss with Mounjaro occurs primarily through reduced appetite and caloric intake rather than increased metabolism. The appetite-suppressing effects often become more noticeable as treatment continues, with steady-state drug levels typically reached after approximately four weeks of treatment.

It is important to maintain realistic expectations: while Mounjaro can lead to clinically meaningful weight reduction in type 2 diabetes patients as shown in the SURPASS clinical trials, these results accumulate gradually. The 2.5 mg starting dose is intentionally low to minimise side effects, and therapeutic effects increase as the dose is titrated upward according to your treatment plan. Remember that in the UK, Mounjaro is licensed specifically for improving glycaemic control in type 2 diabetes, not for weight management. Focus on establishing healthy eating patterns and maintaining adequate nutrition rather than pursuing rapid weight loss, which is neither sustainable nor recommended.

Managing Your Mounjaro Dose at Week 3

During your third week on Mounjaro, you will continue with the 2.5 mg weekly dose unless your prescriber has provided different instructions. According to the Summary of Product Characteristics approved by the MHRA, the standard initiation regimen involves 2.5 mg once weekly for four weeks before increasing to 5 mg weekly. This gradual dose escalation approach minimises gastrointestinal side effects whilst allowing your body to adapt to the medication's effects.

Important dosing considerations for week three:

• Administer your injection on the same day each week to maintain consistent drug levels

• If you miss a dose and it is within 4 days (96 hours) of the scheduled time, take it as soon as possible; if more than 4 days have passed, skip the missed dose and resume your regular schedule

• You may change your injection day if necessary, provided at least 3 days (72 hours) have elapsed since your last dose

• Inject subcutaneously into the abdomen, thigh, or upper arm, rotating injection sites weekly to reduce local reactions

• The injection can be given at any time of day, with or without meals

You should not adjust your Mounjaro dose independently. Dose escalation follows a structured protocol (2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg), with increases occurring at four-week intervals based on glycaemic control, tolerability, and treatment goals. Your diabetes team will determine the appropriate timing for dose increases during follow-up appointments.

If you are experiencing intolerable side effects during week three, contact your prescriber before your next scheduled dose increase. They may recommend remaining at 2.5 mg for an additional period or implementing strategies to improve tolerability.

If you are taking oral contraceptives, be aware that Mounjaro may reduce their effectiveness due to delayed gastric emptying. Use additional barrier contraception for 4 weeks after starting tirzepatide and for 4 weeks after each dose increase.

Combining Mounjaro with a DPP-4 inhibitor (such as sitagliptin, linagliptin) is generally not recommended as it offers no additional benefit. If you are taking insulin or sulphonylureas, your doses may need to be reduced to prevent hypoglycaemia – this should be done under clinical supervision.

Maintain regular contact with your diabetes care team and attend all scheduled monitoring appointments to ensure appropriate treatment progression and early identification of any concerns.

Frequently Asked Questions