Probiotics are the "good" bacteria that help keep your gut healthy, and for most people they cause no trouble at all. Probiotics have been used safely for years. Still, nobody is perfect, and some people notice side effects, usually mild and usually in the first couple of weeks. Here are five to know about, how to manage them, and when to talk to a doctor.
What are the most common side effects of probiotics?
The most common side effects are digestive and short-lived. The NIH notes that studies have generally reported few side effects, though few have examined safety in detail, so it helps to know what is normal and what is not.
1. Gas and bloating
This is the one most people notice. Adding new bacteria, and often prebiotic fiber with them, changes how food is fermented in your colon; prebiotic fibers are fermented by gut bacteria in the colon, and fermentation produces gas. It usually settles as your gut adjusts. This is not a "Herxheimer reaction" or a toxin die-off, which we explain in Taking a Probiotic for the First Time.
How to manage it: take your probiotic with food, increase fiber gradually, drink plenty of water and stay active. Loose clothes help too.
2. Changes in bowel habits
Some people find their stools are looser, or more frequent, for a few days after starting. Probiotics can also make things more regular: in adults with constipation, probiotics added about 1.3 bowel movements a week in a meta-analysis of trials. Either way, your body usually finds its rhythm within a week or two.
How to manage it: take your probiotic with a meal, stay hydrated, and give it time. Diarrhea that is severe, bloody, lasts more than a few days or comes with fever is not a normal adjustment; stop and see a doctor.
Can probiotics cause headaches or allergy-like symptoms?
3. Headaches
Fermented foods, especially aged and protein-rich ones like cheese, cured sausage and wine, can contain biogenic amines such as histamine and tyramine, which are mainly produced in foods by microbes breaking down amino acids. A review of diet and headache found modest evidence that histamine-containing foods may trigger headaches in some people.
How to manage it: if fermented foods seem to trigger headaches for you, a probiotic supplement is a way to get named strains without the amines that build up in aged and fermented foods.
4. Histamine or allergy-like reactions
Some people react to the vasoactive amines in foods. Food intolerances can result from pharmacological effects of vasoactive amines present in foods, such as histamine, producing symptoms that can look like an allergy, such as flushing, a runny nose or itching. Supplements can also contain allergens such as dairy or soy from their growth media or fillers.
How to manage it: check the label for allergens, and if you are sensitive to histamine-rich foods, notice whether fermented foods or a particular product is the trigger. Stop immediately and get medical help for hives, swelling or difficulty breathing.
Who should be cautious with probiotics?
5. Infection in people with weakened immune systems
This is rare but serious. Theoretical risks include systemic infections and excessive immune stimulation in susceptible individuals, and the risk of harmful effects is greater in people with severe illnesses or compromised immune systems. Cases of severe infection have also been reported in premature infants given probiotics.
How to manage it: if you are immunocompromised, seriously ill, recovering from surgery, have a central line, are pregnant or are considering probiotics for a premature baby, talk to your doctor first.
How to choose a probiotic that agrees with you
Look for named strains with research behind them, a clear dose and a short ingredient list. Trust Your Gut Probiotic + Prebiotic Daily Essential contains 16 billion CFU of dairy-free probiotics from 6 acid-resistant strains, plus organic prebiotics, in two capsules a day with food. If you would rather not swallow capsules, Pre + Probiotic Pixies melt in your mouth and deliver 10 billion CFU from 5 researched strains. Our guide to how and when to take your probiotic can help you get off to a smooth start.
