Does iron make you poop?
Nope. Usually the opposite. Iron pills are better known for blocking people up, although some get diarrhea instead. They also turn your poop black, which is normal. Pick yours:
NOPE. Expect firmer, and black.
The most common iron tablet. It carries about 65 mg of iron, above the 45 mg daily limit for people taking iron without a doctor's advice. Constipation is one of its most common side effects.
How much iron is in one tablet
Daily limit for adults: 45 mg (NIH)
The black line is NIH's 45 mg daily limit, counting iron from food and supplements. Doctors prescribe more to treat low iron, and that's fine. Keep iron away from kids: accidental iron overdose is a leading cause of fatal poisoning in children under 6.
Did iron make you go?
The meter says what should happen. Your bowels get a vote too.
Why it backs you up
Constipation is the classic side effect
NIH says high doses of iron supplements, especially on an empty stomach, can cause constipation, nausea, stomach pain and diarrhea. Constipation is the one most people know.
Black poop is normal
MedlinePlus says iron tablets turn stool black, and that's expected. Tarry stool, red streaks or cramping pain are not, and need a doctor.
The tablet size isn't the dose
A "325 mg" tablet is the weight of the iron salt. The iron itself ranges from about 39 mg to 107 mg depending on the salt, and lower doses tend to cause fewer gut problems.
Sources: NIH Office of Dietary Supplements, Iron fact sheet; MedlinePlus, Taking iron supplements; Elemental iron by salt, J Nutr 2023; Rimon et al., Am J Med 2005.