Started a new medicine? What people notice in the bathroom, and what to tell your prescriber
A short guide · Updated September 26, 2026
Starting a medicine or supplement, or changing a dose, can affect your bowel habits. Things slow down, or loosen up, or the timing shifts. What to expect depends on the medicine, the dose and the person. Sometimes it's worth a call. Either way, your prescriber will ask the same few questions, and a couple of weeks of notes answers them better than memory does.
This is general information, not medical advice. Don't stop or change a prescribed medicine on your own. If a change worries you, call the prescriber or a pharmacist. They can tell you what's expected with your medicine and what isn't.
Why the first weeks are different
Many medicines act on the gut directly, or change how fast food moves through it, or change what you eat and drink. How side effects change over time depends on the medicine and the person. The GLP-1 example below describes one pattern; it does not apply to every medicine. It's also why "how has it been since you started?" is such a common question at the follow-up visit, and why it's a hard one to answer from memory.
An example many people recognize: weight-loss and diabetes medicines such as semaglutide or tirzepatide. Their most common side effects are all digestive: reflux, diarrhea, constipation and nausea, according to an endocrinologist at Cleveland Clinic, who says people tend to feel them most during the first three to four weeks, and again after a dose increase. How often each side effect happens depends on the medicine, the dose and the person; the medicine's own label and your pharmacist have the numbers for yours. A 2026 review of the research adds that constipation tends to last longer than the other digestive side effects, while diarrhea is more often on-and-off. This page isn't about any one medicine, though. The same logging habit works for all of them.
Which kinds of medicines tend to change things
Public sources list these as common causes. Your medicine may or may not be on the list; the label and your pharmacist know better than a web page.
| Can slow things down | Antacids that contain aluminum or calcium; iron supplements; opioid pain medicines; some antidepressants; some blood pressure medicines; medicines that relax muscles or calm spasms (NIDDK). |
|---|---|
| Can loosen things up | Antibiotics; antacids that contain magnesium; some medicines used to treat cancer; metformin for diabetes; liquid medicines sweetened with sugar alcohols like sorbitol (NIDDK, MedlinePlus). |
| Can do either | Medicines that change appetite or how fast the stomach empties, including the weight-loss and diabetes medicines mentioned above. Eating and drinking less than usual can, by itself, make stool harder (Cleveland Clinic). |
What to write down for your prescriber
Prescribers don't need an essay. They need dates and a pattern. If you keep a short log, these are the things that turn out to be useful at the follow-up:
- The date you started, and the dates of any dose changes.
- How often you went, and the days you didn't.
- The shape, using the seven Bristol types (1 and 2 harder, 6 and 7 looser). The chart, in plain words.
- Straining, urgency, pain, if any.
- Anything unusual: blood, black or very pale stools, mucus.
- What else changed: how much you ate and drank, new supplements, anything you took over the counter for it, travel.
- Your questions, so you don't forget them in the room.
With that, the conversation is short: "Started on the 3rd. Went every day before, now every two or three days, mostly type 2, some straining, no blood. Drinking less than I used to." Those details can help your prescriber. You can still ask for help if you're unsure how to describe a change.
When to call
Call your prescriber or pharmacist if a bowel change is severe, is getting worse instead of settling, or is still there after a few weeks, or any time you're unsure. NIDDK says adults with diarrhea should talk with a doctor right away for diarrhea lasting more than two days, six or more loose stools a day, a high fever, frequent vomiting, severe pain in the abdomen or rectum, stools that are black and tarry or contain red blood or pus, or signs of dehydration (thirst, dark urine, dry mouth, feeling tired or dizzy). See a doctor for blood in your stool, bleeding from your rectum, or ongoing belly pain, and for constipation that doesn't go away. Get emergency care for heavy bleeding, or bleeding with dizziness, fainting or trouble breathing. Many causes are not serious, but only a clinician can tell.
How a log helps, before and after
The most useful comparison is simple: the weeks before the change, next to the weeks after. If you had a few days of logs before you started, keep going. If you didn't, start now and note the start date; the next dose change becomes your "before and after." Look at the days between bowel movements and the shapes, not at any one day. Day-to-day ups and downs are common, and small differences may not mean much. What you're looking for is a pattern you can describe.
General guidance on fiber, fluids and routine for healthy adults is on our page for people who often feel backed up: what "normal" looks like, and what a two-week log can show you. Whether any of it fits alongside your medicine is a question for your prescriber.
Keeping track, privately
Porcelain is a poop log for iPhone. Tap one of the seven shapes to save, mark "No poop today" on the days without one, and add a note like "dose up" on the day it happens. You can make a free PDF summary of any dates to bring to your appointment, with every log listed. If you like, Porcelain can put the days before and after a change side by side (your first comparison is free; it's part of Porcelain Plus after that). No account, no ads, and your logs stay on your iPhone.
See your pattern after 7 logged days.
This guide is general information, not medical advice. Porcelain is for personal record-keeping and is not intended to diagnose or treat any condition. It does not track medicines or doses. Check with a doctor before making medical decisions. Porcelain is not affiliated with any medicine maker.
Sources
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Symptoms & causes of constipation (medicines and supplements that can cause constipation; when to see a doctor). niddk.nih.gov
- NIDDK. Symptoms & causes of diarrhea (medicines that can cause diarrhea; when to see a doctor right away). niddk.nih.gov
- MedlinePlus (U.S. National Library of Medicine). Drug-induced diarrhea. medlineplus.gov
- Cleveland Clinic. How to manage GLP-1 side effects (Keren Zhou, MD: digestive side effects most significant in the first three to four weeks). September 9, 2026. clevelandclinic.org
- Review of gastrointestinal adverse effects of GLP-1 receptor agonists (constipation lasts longer than other digestive side effects; diarrhea is more often intermittent). PubMed Central, 2026. pmc.ncbi.nlm.nih.gov
- Lewis SJ, Heaton KW. Stool form scale as a useful guide to intestinal transit time. Scandinavian Journal of Gastroenterology, 1997. PubMed
- Manning AP, et al. How trustworthy are bowel histories? Comparison of recalled and recorded information. BMJ, 1976. PubMed
- Centers for Disease Control and Prevention. Symptoms of colorectal cancer. cdc.gov