Metformin Diarrhea Tracker: What to Log for Your Doctor

If you have just started metformin or had the dose raised and your stools have turned loose, it is worth keeping a short daily log. With bowel movements, stool type and dose times written down next to your meals, you can show your prescriber when the loose stools happen and how often. The log is a record for that conversation and does not diagnose anything.

Diarrhea on metformin: what the prescribing information says

Diarrhea is listed among the most common adverse reactions in the FDA prescribing information for metformin. In a label for immediate-release tablets, 53% of patients taking up to 2550 mg a day reported diarrhea versus 12% on placebo, and 6% discontinued because of it. In a label for extended-release tablets, the figures were 10% versus 3%, with 0.6% discontinuing. The labels caution that rates from different trials cannot be directly compared, so these numbers do not rank the two forms.

The patient information in both labels says common side effects such as diarrhea generally go away after you take the medicine for a while, and that taking it with meals can help reduce them. The NHS says most side effects should ease after a couple of weeks, though some can last longer.

What to log for metformin diarrhea

Log each bowel movement soon after it happens:

• Date and time
• Bristol stool type from 1 to 7. Types 5, 6 and 7 suggest diarrhea, while types 3 and 4 are the most ideal
• Urgency, and belly cramping or pain
• Any blood, or black, tarry stool
• Nausea or vomiting

Once a day, add water, urine color, main meals, and anything unusual such as illness, travel or another new medicine. On a separate list, keep the start date, every dose change, and each dose time with a note on whether you took it with a meal.

How to read your own pattern

The NIDDK describes diarrhea as loose, watery stools three or more times a day, or more often than is normal for you. Each week, count the days with three or more loose stools and compare with a typical week before the medicine or before the last dose change.

Start with the dose dates. Did loose stools begin or get worse soon after you started, or after an increase? Then look at meals, and whether the loose days line up with doses taken without food. Watch the weekly count as well, whether it is falling, flat or rising. The label says to tell your doctor about side effects that bother you a lot, last for more than a few weeks, come back after they have gone away or start later in therapy.

Keep other causes in mind too. The NIDDK names viral gastroenteritis, food poisoning and medicine side effects as the most common causes of acute diarrhea. A log that lines up with your doses shows timing, and timing alone does not prove the cause.

A short summary for your prescriber

The NIDDK diagnosis page says doctors may ask how long you have had diarrhea, what your stool looks like, how often it happens, and about your eating and drinking habits and medicines. A one-page summary can cover:

• Tablet type, start date, dose change dates, and dose times with or without meals
• Loose stools per day and per week, before and after, and how often they were type 5 to 7 or urgent
• Belly pain, nausea, vomiting, water and urine color
• Other medicines, recent illness or travel, and any warning signs

Changes to the dose, its timing or the tablet type, and any medicine for diarrhea, are your prescriber’s decision. The NHS says it is important to keep taking metformin and to talk to your doctor if you are having problems with it.

When to get medical help promptly

The NIDDK says adults should talk with a doctor right away about 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, symptoms of dehydration, six or more loose stools a day, or diarrhea lasting more than 2 days. Signs of dehydration include dark yellow, strong-smelling pee, peeing less often than usual and feeling dizzy or lightheaded.

The patient information says getting dehydrated from fever, vomiting or diarrhea raises the chance of lactic acidosis, a rare but serious medical emergency. It says to stop taking metformin and call your healthcare provider right away for symptoms such as feeling very weak and tired, unusual muscle pain, trouble breathing, unusual sleepiness, or unexplained stomach or intestinal problems with nausea and vomiting, or diarrhea. If you have any of the signs in this section, get care first and leave the log for later. 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, tell you what caused a symptom or track your medicine.

• Log each bowel movement with time, Bristol stool type 1 to 7, color, blood or mucus, and an urgency toggle.
• Log belly pain and bloating on a 1 to 7 scale, water toward a daily goal with your own cup size, and food and habits such as coffee, alcohol, dairy, spicy food and stress.
• The day timeline shows what came before and after a hard or loose stool.
• Trends show how often you went and your stool form this week, compared with your usual over the previous four weeks.
• Export a 90-day PDF summary to show a clinician.

It is free, with no subscription, on iPhone and Android in 15 languages. Your diary is stored on your device, and you can start without an account. Some health values, such as stool type, symptoms and manually entered weight, are also sent to PostHog analytics, which is on by default. The analytics switch in settings controls PostHog only. Firebase Analytics receives usage events without those health values. Privacy policy.