GLP-1 Side Effects: The Full List for Semaglutide and Tirzepatide

The GLP-1 medications Pepti prescribes:

Prices are all-in: medication, physician review, refill management and shipping, with no membership fee. Both are compounded by PCAB-accredited, FDA-registered US 503A pharmacies. Compounded medications are not FDA approved; the side-effect rates below come from trials of the approved manufactured products, which contain the same molecules.

The rates below are from the approved weight-management labels: for semaglutide, three placebo-controlled trials in 2,116 adults at 2.4 mg weekly for up to 68 weeks; for tirzepatide, two placebo-controlled trials in 2,519 adults at 5, 10 or 15 mg for up to 72 weeks. They come from different trials in different populations, so a higher figure in one column is not proof that one medication is harder on the stomach.

Semaglutide's label also lists headache (14% against 10%), bloating (7% against 5%), flatulence (6% against 4%), altered taste (1.7% against 0.5%) and fainting (0.8% against 0.2%). Tirzepatide's lists hypersensitivity, mostly rash and itching, at about 5% against 3%.

Reading the list

The placebo columns are the first thing to read. Between 8% and 16% of people on a dummy injection reported nausea, and nearly half of placebo-treated adults in the semaglutide trials reported some gastrointestinal complaint. The amount a GLP-1 adds is the gap between the columns, not the raw figure.

The second thing: on the tirzepatide label, nausea barely changed between 5 mg and 15 mg, and constipation fell at higher strengths. How quickly the dose climbs matters more than where it ends.

GLP-1 is a hormone the gut releases after a meal. The medications copy its effects for days at a time: they prompt insulin release when glucose is high, suppress glucagon, slow stomach emptying and act on appetite centers in the brain. Tirzepatide also activates the GIP receptor, a second gut-hormone receptor.

The stomach-slowing effect is largest after the first dose and after each step up, and smaller with each week at the same strength. That is why side effects cluster around increases, and why approved labels write their escalation schedules specifically to reduce gastrointestinal reactions.

Does the GIP part of tirzepatide change the side effects?

It does not remove them. An animal-level finding suggests GIP receptor activity may moderate nausea signaling, but that is a proposed explanation rather than a settled human result. The side-effect categories, serious risks and contraindications are the same for both medications. The full comparison is in semaglutide vs tirzepatide.

Both approved schedules start low: semaglutide at 0.25 mg weekly and tirzepatide at 2.5 mg weekly, each for four weeks, with increases no sooner than every four weeks after that. Holding at a strength, or stepping back down, is a standard adjustment inside the approved rules. If side effects have not settled, tell your care team before the next step; your physician sets your directions after reviewing how you are doing, and they are printed on your vial. Never change your own dose.

Most people who stop for side effects do so in the first few months, during escalation, which is exactly the window where holding a step helps most.

This advice rests on the mechanism and on clinical experience rather than on trials that randomized people to eating instructions. Pepti physicians can prescribe ondansetron for nausea where they judge it appropriate, though slowing the dose ladder is usually the bigger lever. The longer guide is GLP-1 nausea: how to manage it, and alcohol is covered in can you drink alcohol on semaglutide.

How rare the serious ones are

Both labels describe kidney injury, some needing dialysis, mostly in people whose vomiting or diarrhea led to dehydration. Both describe rare aspiration under general anesthesia or deep sedation because food can remain in the stomach, so tell any surgical, dental or endoscopy team you take a GLP-1 before a planned procedure.

The thyroid warning

Both approved labels carry a boxed warning because these medications caused thyroid C-cell tumors in rodents. Whether they do in people is unknown. The consequence is firm: a personal or family history of medullary thyroid carcinoma or MEN 2 rules out the class. The labels describe routine calcitonin tests and thyroid ultrasound as of uncertain value for screening.

The labels carry a few points that apply specifically to women.

• Birth control pills. Tirzepatide can reduce absorption of oral contraceptives for four weeks after starting and after each increase; the label advises a non-oral method or an added barrier method in those windows.
• Fertility. Weight reduction can bring back ovulation in people who had stopped ovulating, so pregnancy is possible even if it was not before.
• Pregnancy and breastfeeding. Neither medication is used. The semaglutide label advises stopping at least two months before a planned pregnancy because of its long half-life.
• Hair loss. On the semaglutide label it was almost entirely in women and attributed to weight reduction.

More is in do peptides affect fertility.

Bloodwork is not required for any Pepti treatment. If your physician wants labs for your care, they'll ask through your account.

When a GLP-1 is not the right tool

If side effects have been intolerable, or the goal is body composition rather than appetite, there are options that are not GLP-1 receptor agonists and do not slow the stomach, such as tesamorelin, MOTS-c and 5-Amino-1MQ. Their evidence is much thinner. Comparisons are in tesamorelin vs semaglutide and L-carnitine vs GLP-1, and what can be prescribed alongside tirzepatide is in what peptides can you take with tirzepatide.

GLP-1 side effects are among the best-documented of any medication class Pepti prescribes, because the approved products went through large randomized trials with placebo groups. That is why this page can give rates rather than impressions.

The limits are just as clear. The rates belong to the approved manufactured products; a compounded vial has the same molecule but has not been trialed. The two labels cannot be compared head to head. The eating advice is sensible but untested. And events reported after approval have no reliable frequency. Any claim that a compounded version or an added vitamin makes a GLP-1 easier on the stomach has no trial behind it. The deeper safety picture is in is semaglutide safe, is tirzepatide safe and is compounded semaglutide safe.

GLP-1 medications cannot be bought legitimately without a prescription. Products sold "for research use only" have no accountable pharmacy behind their identity, purity, sterility or concentration. The prescription route:

1. Complete a free online intake covering your history, medications and what you want help with.
2. A physician licensed in your state reviews it, usually within 24 hours.
3. If it is appropriate, a state-licensed, FDA-registered US pharmacy compounds it to that prescription. Lot test results are published at /quality/lab-results.
4. It ships refrigerated with ice packs, with sterile syringes and alcohol prep pads, and your directions printed on the vial.
5. Your care team stays reachable for side effects and dose questions. Refills run every 28 days, one vial per fill.

Pepti is cash-pay and does not bill insurance. Step-by-step pages: how to get semaglutide prescribed online and how to get tirzepatide prescribed online.