What is the most common side effect of Zepbound?

Nausea. In the pooled weight-management trials it was reported by 25% of people on 5 mg, 29% on 10 mg and 28% on 15 mg, against 8% on placebo.

How long do Zepbound side effects last?

The label does not give a duration. It notes that gastrointestinal reactions were more frequent while the dose was being increased, which is why the schedule holds each dose for at least four weeks.

Does Zepbound cause hair loss?

Hair loss appears on the label in the list of reactions reported in at least 5% of people treated with Zepbound.

Who should not take Zepbound?

The label contraindicates it for anyone with a personal or family history of medullary thyroid carcinoma, anyone with multiple endocrine neoplasia type 2, and anyone with a known serious hypersensitivity to tirzepatide or its excipients.

Zepbound side effects, straight from the label

The short answer

The label lists twelve reactions reported in at least 5% of people taking Zepbound: nausea, diarrhea, vomiting, constipation, abdominal pain, indigestion, injection site reactions, fatigue, hypersensitivity reactions, burping, hair loss and acid reflux.

Most of them are digestive, most show up while the dose is going up, and a small number of people stop the medicine because of them.

The numbers, by dose

These come from the pooled analysis of two weight-management trials in the prescribing information. The placebo column is the one that makes the rest readable — some of these happen to people who are injecting nothing at all.

How many people had each reaction in the two trials, by dose, with placebo for comparison. The exact figures are in the table.

Reaction	Placebo	5 mg	10 mg	15 mg
Nausea	8%	25%	29%	28%
Diarrhea	8%	19%	21%	23%
Vomiting	2%	8%	11%	13%
Constipation	5%	17%	14%	11%
Injection site reactions	2%	6%	8%	8%
Fatigue	3%	5%	6%	7%

Two things worth noticing. Nausea does not climb steadily with the dose — it is about the same at 10 mg and 15 mg. And constipation runs the other way, more common on the lowest dose than the highest.

How often it gets bad enough to stop

Severe gastrointestinal reactions were reported by 1.7% of people on 5 mg, 2.5% on 10 mg and 3.1% on 15 mg, against 1% on placebo.

Stopping the medicine altogether because of a digestive side effect happened in 3.3% of people on 10 mg and 4.3% on 15 mg, against 0.5% on placebo.

So for roughly nineteen people in twenty on the higher doses, the digestive effects were something to get through rather than a reason to quit.

The boxed warning

Zepbound carries the FDA's strongest warning:

WARNING: RISK OF THYROID C-CELL TUMORS. In rats, tirzepatide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors at clinically relevant exposures.

What that sentence does and does not say matters. It is a finding in rats. Whether tirzepatide causes medullary thyroid carcinoma in people is not known. The label's response to that uncertainty is a hard rule rather than a caution.

Who the label says should not take it at all

Why the dose goes up so slowly

The label starts everyone at 2.5 mg once a week for four weeks, then 5 mg once a week. After that it may rise in 2.5 mg steps, with at least four weeks on the current dose before each increase.

That first 2.5 mg month is not a treatment dose. It exists to let the gut adapt, and the schedule is the main tool anyone has for keeping the effects in the table above manageable.

When to stop and call someone

The label describes reactions that are not part of getting used to the medicine. Contact a clinician promptly for:

Severe stomach pain that does not go away, with or without vomiting — the label warns about pancreatitis.
Pain in the upper right abdomen, fever, yellowing of the skin or eyes, pale stools — gallbladder problems.
Vomiting or diarrhea bad enough that you cannot keep fluids down — dehydration can injure the kidneys.
Swelling of the face, lips or tongue, or trouble breathing — a serious allergic reaction.
Changes in vision, if you have type 2 diabetes.
Low blood sugar, if you also take insulin or a sulfonylurea.
New or worsening depression, or thoughts of harming yourself. Call or text 988 at any hour.

What the label does not tell you

It does not say how long nausea lasts, because that was not measured as a duration. It does not rank the effects by how much they bother people. And it says nothing about compounded tirzepatide, which is a different product made by a pharmacy and is not covered by this labelling at all.