— Side effects

Honest about
what to
expect.

Tirzepatide works — and that comes at a cost. Almost everyone notices something in the first weeks. Usually mild and short-lived, sometimes uncomfortable, in rare cases serious. On this page we explain honestly what's normal, what isn't, what you can do yourself, and when to contact us right away.

— Important to know

Most side effects of Tirzepatide are gastrointestinal and mainly occur in the first 4–8 weeks and after a dose increase. That's why we build up the dose slowly (twelve to twenty weeks). Symptoms then subside in the majority of patients. We monitor your treatment every four weeks and adjust the schedule if needed — no one needs to push through something that feels unsustainable.

— 01 / 04 · Affects more than 1 in 10

Very common.

Gastrointestinal symptoms are the best-known side effects — they are also intentional (feeling full is part of how the medication works), but in the first weeks it can be too much.

Nausea

Up to 30% of users

The best-known effect, mainly in the first 1–3 days after an injection. Usually mild, sometimes troublesome. Almost always subsides after the first 4–8 weeks. With each step up to a higher dose it can briefly return.

What helps: smaller meals, avoiding fatty and heavy food in the first 48 hours, sipping fluids, fresh air, and if really needed an antiemetic (in consultation).

Reduced appetite

Almost everyone

The main effect Tirzepatide is known for: you feel full sooner and have less urge to keep eating. Desirable for most people. Watch out for: eating too little can also become problematic — think less than 1,000 kcal per day, or routinely skipping meals. We discuss at every check-up whether you're getting enough nutrients.

Diarrhoea

10–17% of users

Mainly in the first weeks. Can occur on its own or alternate with constipation. Drink enough (at least 2 litres a day), watch your salt/electrolytes and avoid large amounts of fat or very spicy food. If it persists more than a week, or there's blood — contact us.

Constipation

7–11% of users

Because gut transit slows down, stools can become harder and more difficult to pass. Fibre-rich foods (vegetables, fruit, wholegrain), enough fluids and daily movement help most. For persistent symptoms we can advise a mild laxative.

Fatigue

5–10% of users

Mainly in the build-up phase, and as a result of eating less. Usually temporary. Plan your injection day on a quiet moment of the week — for example a Friday evening — so you don't have to do too much in the first days.

— 02 / 04 · Affects 1 in 100 to 1 in 10

Common.

Less than for everyone, but frequent enough to mention. Almost always manageable.

Abdominal pain / cramps

Common

Cramps or a feeling of pressure in the upper abdomen, mainly after meals. Usually mild and short-lived. Distinction: with persistent severe pain that doesn't fade — especially pain radiating to the back — contact us right away (see below).

Headache

Common

Often combined with too little fluid intake or low blood sugar. Drink enough water, eat something light (a cracker, banana), and check that you haven't been fasting too long. Mild painkiller (paracetamol) is OK in consultation.

Heartburn / reflux

Common

The slower gastric emptying makes heartburn more frequent, especially in the evening. Don't eat just before bed (last meal 2–3 hours before bedtime), use an extra pillow, and avoid coffee/alcohol/carbonated drinks in the first hours after an injection. For persistent symptoms a stomach-acid reducer (in consultation) can help.

Dizziness

Common

Almost always related to eating or drinking too little. Don't drive when dizzy. Eat small, regular portions and watch your fluid intake — if dizziness persists, contact us to evaluate your treatment.

Burping / belching

Common

Unpleasant but harmless. Sometimes with a sulfurous smell or taste. Related to slower digestion. Smaller portions, less carbonation, eat slowly. Disappears for most after the build-up phase.

Reaction at the injection site

Common

Local redness, itching or a small bump around the injection site. Rotate weekly between sites (upper thigh / abdomen / upper arm), and avoid the same spot within four weeks. Almost always resolves within one to two days.

— 03 / 04 · Affects fewer than 1 in 100

Rare, but important to know.

These side effects are uncommon, but you should know what to look out for. If you suspect any of them — contact us right away.

Pancreatitis
(inflammation of the pancreas)

~0.3% of users

The most important serious side effect to know. Symptoms: persistent severe upper-abdominal pain that radiates to the back, often with nausea and vomiting, and tenderness on pressure. Risk factor: alcohol use during the treatment. If suspected: stop the injections, contact our GP or the out-of-hours doctor immediately.

Gallstones / gallbladder inflammation

Rare

Rapid weight loss increases the risk of gallstones — not specific to Tirzepatide, but to the weight loss itself. Symptoms: pain in the upper-right abdomen after fatty food, sometimes radiating to the right shoulder, possibly yellowing of the eyes. Report this to us and your GP.

Allergic reaction

Rare to very rare

Mild reactions (rash around the injection site): change site, usually gone in a few days. Severe reaction — body-wide rash, swollen lips or tongue, breathing problems — is a medical emergency. Stop the injections and call 112.

Hypoglycaemia
(low blood sugar)

Rare, more common with diabetes meds

Tirzepatide alone rarely causes low blood sugar in non-diabetics. Combined with insulin or sulfonylureas the risk is higher — that's why we evaluate your full medication list during the intake.

Thyroid issues

Very rare

Animal studies showed an increased risk of a specific type of thyroid cancer (medullary) — this has not been confirmed in humans, but as a precaution we advise against Tirzepatide for those with a personal or family history of medullary thyroid carcinoma (MTC) or MEN-2 syndrome. We discuss this during the intake.

— 04 / 04 · Practical

What you can do yourself.

Most gastrointestinal symptoms are well managed with simple adjustments. Here are the tips we give most often.

  • Eat smaller portions, more often. Four to six small meals instead of three large ones reduce the pressure on your stomach and lower nausea.
  • Avoid fatty, fried and heavy food in the first 48 hours after your injection. That's the heaviest period. Choose easy-to-digest food — yoghurt, banana, toasted wholemeal bread, chicken, steamed vegetables.
  • Drink at least two litres of water a day. Enough fluid prevents constipation, headache and dizziness. Sip, don't gulp.
  • Eat fibre-rich food against constipation. Wholegrain products, legumes, vegetables, fruit (especially with skin), dried prunes. Add fibre slowly — otherwise you'll feel bloated.
  • Move daily, gently. A 20–30 minute walk helps with both constipation and fatigue. In the build-up phase don't immediately train hard on the day after an injection.
  • Don't lie down right after eating. Wait at least two to three hours between your last meal and bedtime. That spares you heartburn at night.
  • Plan your injection on a quiet evening. Many patients pick Friday evening — any symptoms then fall in the weekend, not in the middle of a workday.
  • Rotate injection sites weekly. Upper thigh, abdomen (away from the navel), upper arm. Not the same spot within four weeks.
  • Avoid alcohol in the first week after a dose increase. Tirzepatide can lower your alcohol tolerance, and alcohol stresses the pancreas.
  • Keep a simple log. A weekly note — weight, symptoms, energy, exercise — really helps at check-ups. Doesn't have to be elaborate.
— Contact us right away

When to call 112 or the out-of-hours doctor.

In the following situations stop the injections and contact our GP (during office hours) or the out-of-hours doctor. For acute symptoms: call 112.

  • Persistent severe upper-abdominal pain radiating to the back, especially with nausea and vomiting (may indicate pancreatitis).
  • Persistent vomiting where you can't keep anything down — for more than 24 hours.
  • Signs of dehydration: barely urinating, very dark urine, dry mouth, drowsiness, fast heartbeat.
  • Allergic reaction: body-wide rash, swollen lips or tongue, breathing problems — call 112 immediately.
  • Pain in the upper-right abdomen after fatty food, possibly with yellowing of the eyes (possible gallstones).
  • Heart palpitations, severe confusion, fainting, or loss of consciousness.
  • When in doubt: always contact us. Better one time too many than one too few.
— Our role

How Lunaris handles side effects.

Side effects aren't a side issue — they determine whether a treatment stays manageable. That's why we monitor them actively, not just when you call.

At every four-weekly check-up we explicitly discuss which symptoms you're experiencing, how severe they are, and whether the schedule needs adjustment — slower build-up, a temporary pause, or in rare cases switching to a different medication. In between appointments you can reach us digitally, also outside office hours. We want your treatment to be effective and liveable.

More on how a treatment works as a whole on the Treatments page. Specific questions about side effects, holidays, sport and alcohol are in our extended FAQ.

— Worried or unsure?

A treatment never has to be alone.

Send a message via the contact form — we reply within one working day. For current patients with urgent symptoms: call your location during office hours, or the out-of-hours doctor outside that.

Ask a question → Call your location