Can Probiotics Cause Harm?

Forty trillion. TRILLION. That’s how many bacteria cells live in an adult’s colon (large intestine). When you hear the word “bacteria,” you might think about infections, contamination, or sickness. However, certain “good” bacteria naturally exist within the human gut. This huge army of bacteria cells — also called the gut microbiota — is essential in helping with digestion, immune system function, and ridding your body of harmful germs.

Key takeaways:
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    Probiotics are found in many fermented foods and are also available as dietary supplements.
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    Probiotic products are generally safe for most people when used according to the instructions on the product label.
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    Side effects of probiotics may include abdominal discomfort, cramping, gas, nausea, or soft stools.
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    Probiotic supplements are not recommended for people with certain health conditions.

These bacteria are also available as dietary supplements known as probiotics. Probiotics are living microorganisms that, when consumed in proper amounts, are beneficial to the host organism. While generally considered safe, conflicting evidence exists regarding their effectiveness and may even cause harm in certain high-risk individuals.

What are probiotics?

Probiotics are live microorganisms (mainly bacteria) similar to beneficial microorganisms naturally found in the human gut. Humans have unknowingly consumed probiotics for thousands of years via fermented foods. For example, bread, wine, cheese, and yogurt all contain bacterial species that exist naturally within the human body.

Probiotics have been developed as powders, capsules, tablets, liquids, and food additives. Probiotic manufacturers mainly focus on the following three species of bacteria, each having a unique set of considerations and uses:

  • Lactobacillus
  • Saccharomyces
  • Bifidobacterium

Probiotics – benefits & risks:

The Food and Drug Administration (FDA) considers probiotics as dietary supplements. However, unlike medications, dietary supplements do not require clinical testing for effectiveness. As a result, conflicting evidence exists regarding using probiotics for various medical conditions.

Benefits of probiotics

Yet, researchers have identified several cases in which probiotics may provide health benefits, including the following:

Promoting normal bacteria in the body. Various factors can interfere with the normal growth of your gut microbiota. For example, when you take antibiotics to treat an infection, the antibiotic may wipe out the “friendly” bacteria and the bacteria causing the infection. Therefore, healthcare practitioners commonly recommend probiotics during or after antibiotic treatment — to restore the “good” bacteria that normally live in the gut.

Irritable bowel syndrome (IBS). Certain probiotic strains have demonstrated usefulness in reducing the severity of IBS. However, not every case of IBS may benefit from probiotics, so those experiencing IBS should consult a physician before use.

Stopping or preventing diarrhea. In specific settings, probiotics have shown promise in limiting the severity and duration of diarrhea. However, the potential benefit does not apply to all causes of diarrhea, and individuals should consult with a healthcare provider before using probiotics to treat it.

Potential risks of probiotics

Just as there’s limited concrete evidence regarding the benefits, information available about the risks of probiotics is lacking. According to reports, probiotics may cause side effects, such as:

  • Mild abdominal cramping
  • Gas
  • Nausea
  • Soft stools

Rarely, people with weakened immune systems may be susceptible to infections caused by probiotics. For example, those undergoing chemotherapy or taking medications that suppress the immune system may be vulnerable to probiotic-related infections.

Who should take probiotics?

There isn’t a clear answer on who should take probiotics. While probiotics are available without a prescription, it’s still best to seek your doctor’s advice if you have questions or concerns about probiotic selection and dosage.

People who are taking or recently took antibiotics may benefit from probiotics. In addition, some experts suggest probiotics to help ward off fungal infections, such as yeast infections, that sometimes occur with antibiotic use.

How to take probiotics

Each probiotic and manufacturer provides instructions for use. Be sure to read the directions on the product’s packaging and label before use. The instructions may vary with the reason for use.

For illustrational purposes, we've prepared examples of how two popular probiotic products can be taken for different needs:

  • Culturelle Digestive Health Capsule: 1 capsule per day should be taken for daily use; alternatively, 1 capsule in the morning and 1 capsule at bedtime can be taken for treating occasional digestive upset.
  • Visibiome Packets: 4–8 packets dissolved in water and taken daily are recommended to treat ulcerative colitis; for irritable bowel syndrome (IBS), the daily dose is 0.5–1 packet dissolved in water per day.

Who should avoid probiotic supplements?

According to the FDA and the product labels of many probiotics, people with the following conditions or factors should not take probiotic supplements:

Weakened immune system

This includes people receiving chemotherapy or radiation and individuals taking drugs to suppress the immune system for transplants or autoimmune diseases. For example, probiotics may increase the risk of infection in people with compromised immune systems.

Structural heart problems

The FDA recommends avoiding probiotic supplements if you have an abnormal heart valve or have had a heart valve replacement. People with structural heart problems or a history of endocarditis may be at increased risk of heart valve infection.

Central line or port

People with a central line or port for intravenous access or medication administration should not receive probiotics, especially hospitalized patients receiving critical care. It’s thought that probiotic use in these groups could increase the risk of severe infections.


There isn’t enough evidence to evaluate the safety of probiotic use during pregnancy.


People who’ve had an allergic reaction to probiotics or yeast should not take probiotic supplements.

Should you take probiotics?

Probiotics can improve or replenish the human body's natural bacteria stores. These supplements are generally safe for most people, but more research is needed to confirm widespread benefits. Talk to your healthcare provider for personalized medical advice about whether you should take probiotics and, if so, which strains of bacteria and dosage is best for you.


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Haluk ISIK Haluk ISIK
prefix 1 month ago
Good information, but it should have mentioned prebiotics as well.