Probiotics: Possible Side Effects And How To Take Them Safely

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Medical News TodaySubscribeCan probiotics cause side effects?

Medically reviewed by Kelsey Nank, PA-C — Written by Cathleen Crichton-Stuart — Updated on May 30, 2025

Overview
Benefits
Side effects
Taking them safely
Summary

Probiotics are healthful strains of live bacteria and yeast that may provide a range of benefits. However, there are also possible side effects of probiotics, such as bloating and gas. It may increase the risk of infection in those with a weakened immune system.

Trillions of bacteria and other microorganisms live in the gut. Scientists refer to this community of gut-dwelling organisms as the gut microbiota.

Research indicates that this microbiota plays an important role in digestion and gut health, while supporting the immune system, for example.

Some bacteria benefit their human hosts, while other types cause harm. Disturbing the natural balance of bacteria in the gut can lead to digestive problems, infections, and other issues.

What are probiotics?

A bowl of yogurt, which contains probiotics. 2 — Ernesto r. Ageitos/Getty Images

Studies suggest that consuming probiotics can provide more healthful bacteria, which may help restore the balance of the gut microbiota.

Some yogurts, supplements, and fermented foods, including kefir, sauerkraut, and tempeh, contain probiotics.

The most common probiotics that manufacturers add to commercial products are species of Bifidobacterium and Lactobacillus bacteria.

A range of probiotic supplements and yogurts are available to purchase online.

Benefits of probiotics

Research suggests that probiotics may help manage gastrointestinal conditions, including irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD).

Many people use probiotics to help treat episodes of diarrhea and constipation.

There is also evidence that probiotics may help with:

eczema
obesity
insulin resistance
type 2 diabetes
nonalcoholic fatty liver disease
improving immune system function

Possible side effects

Though taking probiotics may provide various benefits, it can also cause side effects, including:

Digestive symptoms

When first using probiotics, some people experience gas, bloating, or diarrhea. Changes in the gut microbiota can result in bacteria producing more gas than usual, which can lead to bloating.

However, these side effects usually clear up within a few days or weeks of taking the probiotics. If the symptoms persist, speak with a doctor, who can explore the possible causes. In some cases, the doctor may recommend switching to a different probiotic.

Skin problems

In rare cases, probiotics may cause skin rashes or itchiness.

Authors of a 2018 review found that two study participants who took probiotics to treat IBS reported an itchy rash as a side effect. This led one participant to drop out of the trial.

If a rash or severe itching occurs, stop using the probiotic. Check the product’s labeling for any possible allergens, and see a doctor if the rash is severe, persistent, or it accompanies other concerning symptoms.

Once the rash has cleared, a person can try a different product or strain of probiotic.

Allergy risk

Anyone with an allergy or intolerance to gluten, soy, eggs, dairy, or lactose may need to exercise caution when choosing probiotics.

As with any supplement, always check ingredient lists to ensure that there is no risk of an allergic reaction. Some manufacturers offer allergen-free probiotics.

Anyone experiencing symptoms of an allergic reaction should stop using the probiotic immediately. Seek medical care if the reaction is severe.

Increased risk of infection

Although probiotics are generally safe to use, findings of a review from 2017 suggest that children and adults with severe illnesses or compromised immune systems should avoid using probiotics.

Some people with these conditions have experienced bacterial or fungal infections as a result of probiotic use.

If a person has a condition that affects their immune system, they should speak with their doctor before taking probiotics.

Also, anyone using antifungal medication should wait until the infection has cleared up before taking probiotics.

Small intestine bacterial overgrowth (SIBO)

The small and large intestines usually contain different types of bacteria. SIBO occurs when bacteria from the large intestine start growing in the small intestine.

The large intestine predominantly contains anaerobic bacteria, which do not require oxygen and live by fermenting indigestible carbohydrates from plant-based foods as they pass through the gut.

Symptoms of SIBO are similar to those of IBS, including gas, bloating, and diarrhea. SIBO can also cause brain fogginess and short-term memory problems.

Not everyone with IBS has SIBO, but the overgrowth is more common in people with IBS. SIBO also frequently develops in females and older people.

Experts do not fully understand what causes the overgrowth, but it may result from reduced gut motility, which slows the passage of food through the gut. This can cause fermentable carbohydrates to remain in the small intestine for longer.

Results of a 2018 study indicate a possible link between SIBO and probiotic supplementation in people with brain fogginess. The researchers found that symptoms improved when participants stopped taking probiotics and started taking antibiotics.

Anyone with SIBO symptoms should consult a doctor.

Antibiotic resistance

Rarely, probiotic bacteria can contain antibiotic-resistant genes. They can pass these genes on to other strains of bacteria, including the harmful strains that cause infections.

However, manufacturers systematically test commercial probiotics stains for the presence of antibiotic resistance. To reduce the risk of consuming antibiotic-resistant bacteria, always source probiotics from trusted, reputable manufacturers.

How to take probiotics safely

Little evidence suggests that a person can overdose on probiotics. However, a person should always read the labeling carefully and not exceed the manufacturer’s recommended dosage.

The optimal dosage can vary, depending on a person’s health and the type of probiotic product.

If a probiotic causes any side effects or symptoms, consider reducing the dosage or refraining from taking the product.

Summary

Probiotics are beneficial strains of live bacteria or yeast. Regularly taking probiotics can help restore the natural balance of the gut microbiota. It may also help treat a number of health conditions, including IBS and IBD.

Probiotics are generally safe, and any side effects are usually mild and short-lived. However, if a symptom is causing concern, consider reducing the probiotic’s dosage, trying a different strain, or stopping use altogether.

Consult a doctor about any severe or persistent side effects.

Before using any probiotic product, read the instructions carefully and do not exceed the maximum dosage. People with allergies should also check the labeling for potential triggers.

Q:

Are there alternatives to probiotic supplements?

A:

Probiotics are found in many common foods, and a variety of types of healthy bacteria are available from the diet alone.

If you are considering taking probiotic supplements, research your manufacturer. The FDA do not monitor supplements, so it is wisest to buy from a reputable drugstore or health food chain. Always check expiry dates.

Check the colony forming units (CFU) on the bottle to see the amount of bacteria in the dose, and follow the manufacturer’s guidelines for how much to take. Some probiotic supplements require storage in a refrigerator.

Debra Rose Wilson, PhD, MSN, RN, IBCLC, AHN-BC, CHT Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

GastroIntestinal / Gastroenterology
Nutrition / Diet

How we reviewed this article:

SourcesMedical News Today has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

Agamennone V, et al. (2018). A practical guide for probiotics applied to the case of antibiotic-associated diarrhea in the Netherlands.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6091175/
Ghoshal UC, et al. (2017). Small intestinal bacterial overgrowth and irritable bowel syndrome: A bridge between functional and organic dichotomy.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5347643/
Hungin APS, et al. (2018). Systematic review: Probiotics in the management of lower gastrointestinal symptoms — an updated evidence-based international consensus.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5900870/
Markowiak P, et al. (2018). Effects of probiotics, prebiotics, and synbiotics on human health.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5622781/
Rao SSC, et al. (2018). Brain fogginess, gas, and bloating: A link between SIBO, probiotics, and metabolic acidosis.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6006167/
Rondanelli M, et al. (2017). Using probiotics in clinical practice: Where are we now? A review of existing meta-analyses.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5730384/
Valdes AM, et al. (2018). Role of the gut microbiota in nutrition and health.https://www.bmj.com/content/361/bmj.k2179
Vitetta L, et al. (2017). Probiotics, D-lactic acidosis, oxidative stress and strain specificity.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5570418/

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Medically reviewed by Kelsey Nank, PA-C — Written by Cathleen Crichton-Stuart — Updated on May 30, 2025

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