Most people are nervous before the first injection and underwhelmed after it. That is the normal pattern. Here is what the first seven days on 2.5mg usually look like, what to do about it, and the small number of things that mean you should ring us.
Day 1: the injection
The pen is a single use KwikPen with a short, fine needle. Pinch the skin on your stomach (at least five centimetres from the belly button), thigh or upper arm, press the pen on, and hold for ten seconds until the second click. It takes about as long as reading this sentence. A small sting or a drop of blood is normal. Pick a day and an approximate time you can keep every week.
Nothing much happens on day one. A few people feel slightly sick or light headed in the evening. Eat a normal, lighter meal and go to bed.
Days 2 to 3: appetite drops
This is when most people first notice it. You sit down to a meal you would normally finish and find you are done halfway. Food noise, the constant background thinking about eating, often goes quiet. Some people describe it as the first time in years they have forgotten to eat.
Nausea peaks here if you are going to get it. It is usually mild, comes in waves, and is worse after large or fatty meals. Burping and a full, heavy feeling after eating are common because the stomach is emptying more slowly.
Days 4 to 5: your gut adjusts
Bowel habits change one way or the other. Loose stools and constipation are both common. Drink more water than you think you need. Tiredness is reported by a lot of people in week one, partly the medicine and partly because you are eating less. It settles.
Days 6 to 7: settling
By the end of the week most side effects have eased. Appetite stays lower. Your second injection is due on day 8, the same day as the first. Some people get a smaller repeat of the nausea on the day after each injection for the first month. That is expected.
What to eat and drink
- Smaller plates. Eat slowly. Stop at full, not at empty.
- Protein with every meal. Eggs, fish, chicken, lentils, yoghurt.
- Keep fatty, fried and very sweet food to a minimum this week. They are the biggest nausea triggers.
- Two litres of water a day, more if you have loose stools.
- Alcohol is not banned but it hits harder on an emptier stomach. Go carefully.
- Plain foods help if you feel sick: toast, crackers, rice, bananas, ginger tea.
Storing the pen
Fridge, 2 to 8 degrees, in its box. If you travel, the pen can stay out of the fridge below 30 degrees for up to 21 days in total. Never freeze it. Each pen is single use: one injection, then into the sharps bin that comes with your order.
When to call us the same day
- Vomiting or unable to keep fluids down for more than 24 hours.
- Severe or constant stomach pain, especially if it spreads to your back. This can be pancreatitis and needs checking.
- Yellow skin or eyes, pale stools, dark urine.
- Rash, swelling of the face or lips, difficulty breathing. Call 999 if breathing is affected.
- Shaking, sweating and confusion if you also take insulin or a sulfonylurea for diabetes, which can mean low blood sugar.
Anything else, message the clinic through your account or ask in either branch. Mild nausea, tiredness and loose stools in week one do not need a call unless they are getting worse rather than better. You can also report any side effect to the MHRA through the Yellow Card scheme.
What happens after week four
After four weeks on 2.5mg you move to 5mg, which is the first real treatment dose. Our check in email arrives before your repeat is due and the prescriber reviews every reorder. How the doses work from there is covered in Mounjaro doses explained.
Sources: Mounjaro Summary of Product Characteristics and Patient Information Leaflet (eMC); NHS, tirzepatide (Mounjaro); BNF tirzepatide monograph; MHRA Yellow Card.