Probiotic Side Effects: Gas, Bloating, Histamine and Other Reactions and When to Stop and Ask

Urgent first

Get medical care promptly for fever, chills or feeling seriously unwell after starting a probiotic, for signs of a serious allergic reaction, or if you are immunocompromised, have a central line or are caring for a premature baby. In the US, call 911 for an emergency. A drug reference for a yeast probiotic says a very serious allergic reaction is rare but needs medical help right away, and lists signs of infection such as a sore throat that does not go away, fever and chills as reasons to tell a doctor right away. [1]

The NHS (UK) lists bloody diarrhoea, diarrhoea for more than 7 days or vomiting for more than 2 days, and worry about a baby under 12 months among reasons to seek urgent advice. [2] Those are signs of illness that need assessment whether or not a probiotic is involved.

What counts as a common side effect

Many people notice nothing. The NHS says that if you have a healthy immune system, probiotics shouldn't cause any unpleasant side effects. [3] NCCIH adds that few studies examined safety in detail, so how often side effects occur is not well known. [4] A 2015 review said safety outcomes are inconsistently reported in clinical trials. [5]

Evidence labels used here: reported in trials (a trial or review recorded it), drug reference statement, and Proper evidence not found.

The Cochrane review also noted that authors of 28 included studies had a probiotic company affiliation or funding, which is worth bearing in mind when reading trial safety summaries. [6] Trial amounts are study amounts, not advice.

Gas and bloating

NIDDK explains that undigested carbohydrates reach the large intestine, where bacteria break them down and create gas. [9] Products can also contain other ingredients: a drug reference notes some products contain fiber or inulin, and that liquid products, foods, powders or chewable tablets may contain sugar or aspartame. [1] The NHS advises people with IBS to avoid products containing the sweetener sorbitol. [10] Reading the ingredients matters: see Reading supplement labels.

NIDDK advises talking with your doctor before using supplements, probiotics or complementary approaches for gas. [11] For what trials show for bloating and SIBO, see Probiotics for bloating, gas and SIBO.

Histamine and headache: what we looked for

Some people ask whether probiotics raise histamine or trigger headaches. Proper evidence not found. We searched PubMed for human studies linking probiotic supplements to histamine symptoms or headache (terms including histamine, biogenic amines, histamine intolerance, gut microbiota and probiotics) and checked general web results. The PubMed results were food-science and laboratory papers, not trials in people taking probiotic supplements; the web results were mostly commercial pages and were not used. One dose-response trial recorded bloating, flatulence and headache in a diary, but its abstract does not report a separate headache result. [8] That is not evidence either way. For histamine in fermented foods, see Fermented foods safety.

When to stop and ask

We cannot tell you to stop or continue; that depends on the person. Reasonable points to raise with a pharmacist or clinician: symptoms that last or get worse, any fever, a reaction that looks allergic, or if you take medicines or have a health condition. See Probiotic safety, side effects quick reference and Side effects, allergic reactions and reporting. Never stop a prescribed medicine because of a probiotic side effect without speaking to the prescriber.