Does milk thistle cause diarrhea, bloating or constipation?

Yes — diarrhea is one of the most commonly reported side effects of milk thistle, alongside nausea, headache and skin reactions. It's usually described as mild, and it's the symptom that tends to show up more as the dose gets higher, according to the human safety data available.

What the research reports

A 2019 review of silymarin's safety and toxicity found gastrointestinal effects — specifically nausea and diarrhea — were the main symptoms that increased as the dose rose, even in trials using doses well above what most commercial labels sell. A separate reference monograph on milk thistle lists diarrhea, headache and skin reactions as the most commonly reported side effects in adults at ordinary doses, and notes rare but real severe allergic reactions, including in people allergic to ragweed, daisies, artichokes or other plants in the same family. See milk thistle side effects for the complete list this page draws from.

Other symptoms people ask about

Gas, bloating, heartburn and dizziness aren't specifically named as documented milk thistle side effects in the two safety sources this page relies on — only diarrhea, nausea, headache and skin reactions are called out by name. That's a gap in what's been reported, not proof those symptoms can't happen; general gastrointestinal upset is described broadly enough that milder, related symptoms could plausibly fall under the same umbrella. Itching would most likely register as one of the documented "skin reactions" rather than a separate category. Bleeding and hair loss aren't mentioned in either source reviewed here.

Questions people ask

Does milk thistle make you poop?

It can contribute to diarrhea in some people, reported as one of the more common side effects, particularly at higher doses. It isn't studied or marketed as a laxative; diarrhea there is a documented side effect, not an intended use.

Is milk thistle a laxative?

No. Milk thistle hasn't been studied or marketed for that purpose — diarrhea shows up in the safety data as an unwanted side effect at higher doses, not as a deliberate bowel-movement aid.

Does milk thistle cause gas or bloating?

Neither is specifically named in the safety sources this page reviewed. Documented gastrointestinal effects are nausea and diarrhea; if gas or bloating happens, it likely falls under the broader "gastrointestinal symptoms" description these reviews use rather than being its own separately studied effect.

Can milk thistle cause nausea or heartburn?

Nausea is specifically documented as one of the more common side effects, especially at higher doses. Heartburn isn't named in the sources reviewed here.

Can milk thistle cause dizziness, itching or bleeding?

Dizziness and bleeding aren't documented in the safety sources this page reviewed. Itching would most likely fall under the "skin reactions" that are listed as a commonly reported side effect, and can, rarely, be part of a severe allergic reaction — see who should not take milk thistle for who's at higher risk of that.

Can milk thistle cause hair loss?

No human trial or safety review this page found reports hair loss as a milk thistle side effect.

When to talk to a doctor

Mild diarrhea or nausea that doesn't resolve, or any sign of an allergic reaction — hives, swelling or trouble breathing — is a reason to stop and check with a doctor, especially if you have a known allergy to ragweed or related plants.

Related reading: milk thistle side effects, who should not take milk thistle, and how much milk thistle should you take a day.