GLP-1 Diarrhea: What to Log and When to Call

Loose stools after starting semaglutide (Wegovy, Ozempic) or tirzepatide (Mounjaro, Zepbound), or after moving up a dose, are common: all four US labels list diarrhea among the most common side effects. Write down for a few days how many loose stools you had, how much you drank and when the dose last changed, and you’ll have specific numbers to give your prescriber when you call.

When GLP-1 diarrhea tends to show up

The Ozempic label says the majority of nausea, vomiting and diarrhea reports occurred during dose escalation. The Mounjaro and Zepbound labels say the same and add that these reports decreased over time. The Wegovy label tells doctors to monitor kidney function in patients with side effects that could lead to fluid loss, especially when starting the medicine and raising the dose.

Diarrhea in each label’s trial table:

Medicine	People in the trials	Diarrhea on the medicine	On placebo
Wegovy 2.4 mg injection	Adults with obesity or overweight	30%	16%
Ozempic 0.5 mg / 1 mg	Adults with type 2 diabetes	8.5% / 8.8%	1.9%
Mounjaro 5 / 10 / 15 mg	Adults with type 2 diabetes	12% / 13% / 17%	9%
Zepbound 5 / 10 / 15 mg	Adults with obesity or overweight	19% / 21% / 23%	8%

The trials enrolled different people, so the table can’t rank the medicines against each other. The Zepbound figure also counts reports of frequent bowel movements.

A dose-increase week next to a settled week

The NIDDK describes diarrhea as loose, watery stools three or more times a day, or more often than is normal for you. On the Bristol chart, types 5, 6 and 7 suggest diarrhea. So count type 5 to 7 stools per day and set them against a week when nothing changed. The numbers below are made up to show the layout.

Week (example)	Settled dose	First week on a higher dose
Days with 3 or more type 5 to 7 stools	0	3
Most loose stools in one day	2	5
Urgent trips	1	6
Water, average per day	1.8 L	1.3 L
Pee color	Pale yellow	Dark yellow on 2 days
Belly pain	None	Cramps on 2 days

In the right column, loose stools went up while water went down and pee got darker. Together those can be signs of losing fluids, which the Medication Guides warn may lead to kidney problems, so it is a reason to call rather than wait for the next appointment.

One day from the log

Again a made-up example, this time the third day after a dose increase:

Time	Entry
06:50	Type 6, urgent
07:30	Water 300 mL, toast
09:15	Type 7, urgent, mild cramps
11:00	Pee dark yellow, water 500 mL
13:00	Soup, sugar-free gum afterwards
16:40	Type 6
20:00	Note: day 3 on the new dose

The gum is there on purpose. The NIDDK says sugar alcohols in sugar-free candy and gum may cause diarrhea in some people, and names viral gastroenteritis, food poisoning and medicine side effects as the most common causes of acute diarrhea. Note a stomach bug at home or a takeaway meal too, since a loose day after a dose change does not prove the medicine caused it.

Keeping up with fluids

The Medication Guides for all four medicines say diarrhea, nausea and vomiting may cause a loss of fluids that can lead to kidney problems. They say it is important to drink fluids, and to tell your healthcare provider right away if nausea, vomiting or diarrhea does not go away. The NHS suggests lots of fluids such as water, in small sips if you feel sick, says fruit juice and fizzy drinks can make diarrhoea worse, and says a pharmacist can recommend oral rehydration solutions.

For dehydration, the NHS advises an urgent GP appointment or NHS 111 if you feel dizzy when you stand up and it does not go away, or you have dark yellow pee or are peeing less than normal.

When to stop logging and get help

• Severe pain in your stomach area that will not go away, with or without vomiting, sometimes felt through to your back. The Medication Guides say to stop using the medicine and call your healthcare provider right away, because it can mean an inflamed pancreas. Upper stomach pain, fever, yellowing skin or eyes and clay-colored stools are listed as possible gallbladder symptoms. The Ozempic, Mounjaro and Zepbound guides say to tell your provider right away, and the Wegovy guide says to call your provider.
• Black, tarry stools or stools with red blood or pus, severe pain in the abdomen or rectum, frequent vomiting, high fever, a change in mental state, signs of dehydration, six or more loose stools a day, or diarrhea lasting more than 2 days. The NIDDK says adults should talk with a doctor right away about any of these.
• Being sick so often you cannot keep fluids down, or diarrhoea lasting more than 7 days. The NHS says to call 111 now.
• Signs of dehydration together with confusion, being sleepier than normal or hard to wake. The NHS says to call 999 or go to A&E.

Outside the UK, get urgent medical advice for the symptoms above. For dehydration with confusion, unusual sleepiness or difficulty waking, call your local emergency number or go to an emergency department right away.

For side effects that bother you or don’t go away, the NHS pages on semaglutide and tirzepatide say to speak to a pharmacist or doctor and to keep taking the medicine unless you’re advised to stop. That is general advice and does not replace the Medication Guide instruction above to stop and call right away for severe stomach pain that will not go away. Any change to your dose is your prescriber’s decision. This article is general information, not medical advice.

How bellySignal helps

bellySignal is a self-recording diary, not a medical device. It does not diagnose or tell you what caused a symptom.

• Log each bowel movement with its time, Bristol type 1 to 7, color, blood or mucus, and urgency. Black and clay-colored stools are both on the warning lists above, so color is worth the extra tap.
• Log pee color on a 1 to 8 hydration scale and water in cups or mL, so a day of low intake and dark pee is easy to spot.
• Add foods and notes. There is no separate field for dose amounts, so write a dose change as a note on the day it happens.
• Put your GLP-1 medicine on the Meds & supplements list and tap it each time you take a dose. Reminders are optional and repeat every day at the times you set, so they don’t fit a weekly injection schedule.
• Export a 90-day PDF summary for your clinician. It also shows, for up to 10 meds and supplements, how many days each was logged.

It is free, with no subscription, on iPhone and Android. The diary is stored on your device, and you can log without an account. Selected health values (stool type, symptoms and any weight you enter) are sent to PostHog by default, and the settings switch controls PostHog only. Firebase Analytics receives usage events without those health values and stays on when the switch is off. See the privacy policy.