Side Effects of Probiotics

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side effect of probiotics

Probiotics are living microorganisms that can bring several health benefits to the human body supporting digestive health, boosting immunity, and promoting overall well-being. Although they are generally considered safe, like any other medications, supplements, and healthy food, they also have some adverse effects when consumed in incorrect amounts, timing, or when somebody has an underlying medical condition. This article will summarise how probiotics might have some unwanted side effects for us. 

Factors Influencing Probiotic Side Effects

Several factors can influence the likelihood and severity of probiotic side effects are;

  1. The dosage 
  2. The duration of probiotic use
  3. The type of probiotic supplement used and
  4. Individual differences in gut flora 

(a) Dosage 

It is more problematic in people taking probiotic supplements rather than probiotic-rich food since most supplements are small, well-flavored, and easy to administer. As a result, it is susceptible to take multiple times a day or multiple doses at a time.

(b) Duration

When taken for an extended period of time like for years, probiotics can also bring harmful side effects, particularly in the digestive system including the gut. Since they are in fact, “living microorganisms”, they can multiply and enter our bloodstream giving harmful side effects.

Such probiotic-related side effects are more susceptible in people with certain medical conditions like inflammatory bowel disease or lactose intolerance. 

(c) Types of Probiotic supplements used 

Since there are several brands and strains of probiotic supplements in the market, the side effects might vary according to the organisms they contain. For example, some strains are prone to cause gut symptoms and some may cause allergic symptoms. 

(d) Individual variation in gut flora

It is the natural difference in gut microflora content. The gut of some people has a higher power of multiplication of probiotics and hence might have the desired effect with a lesser amount. When such people take an excessive amount of probiotics, they are prone to have side effects. 

Common Side Effects of Probiotics

Gut Upset

common side effect of probiotics

Since their action starts mainly in our gut, the main symptoms of common adverse effects include gas, bloating, upset stomach, diarrhea, and constipation. 

Why and when does it commonly occur?

Such unwanted symptoms might occur as a result of the introduction of new bacteria into the gut, or due to changes in the composition of existing gut bacteria. This is because the gut which is formerly familiarized with an environment containing a relatively small number of probiotics is abruptly responding to the healthy organisms that we consume. 

Generally Mild and Self-Limiting

These symptoms are generally mild and self-limiting and rarely persist for more than two weeks. However, in some individuals, such symptoms cause marked discomfort and may persist for several days or even weeks. In some cases, adjusting the dose, type, or brand of probiotic supplement can help to alleviate these symptoms.


The science behind probiotic-related headache

Some probiotic-rich foods, like yogurt, sauerkraut, and kimchi, contain biogenic amines which result when protein-containing foods are fermented by bacteria. The most common amines found in probiotic-rich foods include histamine, tyramine, tryptamine, and phenylethylamine.

Nerve stimulants disturb blood flow to the brain

Amines can excite the central nervous system, increase or decrease blood flow and may trigger headaches in people sensitive to the substance 

A more in-depth scientific study is needed

A study conducted by the National Institute of Health indicate that low-histamine diets reduced headaches in 75% of participants. However, a review of 10 controlled studies found no significant effect of dietary amines on headaches.

Therefore, more detailed research is needed to determine whether or not amines can be direct triggers of headaches or migraines in some people.

Rash and Allergic Reactions

Why might it occur?

Probiotic processing produces histamine

Some bacterial strains used in probiotic supplements and fortification of food can produce “histamine” inside our gut and stomach.

Histamine can cause dilation of our blood vessels and can cause redness and swelling in the affected area, and can also trigger allergy symptoms such as itching, watery eyes, runny nose, or even trouble breathing in severe cases.

Only susceptible individuals

Normally, histamine that is released in the gut is degraded by some natural enzymes to avoid such symptoms. But, in some susceptible individuals, they are not degraded and may cause allergic reactions. 

Take precautions when consuming those if you have a history of allergic reactions

Some histamine-producing probiotic strains include Lactobacillus buchneri, Lactobacillus helveticus, Lactobacillus hilgardii and Streptococcus thermophilus.


Infections may not generally occur due to probiotics. However in certain people with weakened immune systems, prolonged hospitalizations, venous catheters, or those who have undergone recent surgeries, they might cause infection when they enter the bloodstream.

Extremely rare

However, the risk of developing an infection is extremely low, and yet no serious infections have been reported in clinical studies. 

Research has estimated that only about one in one million people who take probiotics containing Lactobacilli bacteria might develop an infection. The number is even smaller for yeast-based probiotics, with only about one in 5.6 million. 

Tips for reducing probiotic side effects

tips to reduce probiotics side effects
  • Follow the recommended dosage instructions: Taking too much of a probiotic supplement can increase the risk of gastrointestinal symptoms. Follow the recommended dosage instructions and it is advisable to start with a low dose, and gradually increase it as needed.
  • Be aware of potential interactions: Probiotic supplements can interact with certain medications or health conditions as described above. Should you have a medical condition or are taking medication, always talk to your healthcare provider before taking a probiotic supplement.
  • Consider a targeted probiotic supplement: Some probiotic supplements are designed to target specific health conditions, such as digestive disorders or vaginal health. Such specifically tailored probiotics might be a better choice than a general probiotic supplement.
  • Monitor for symptoms: In case you experience any unusual symptoms after starting a probiotic supplement or some probiotic-containing food, it is recommended to stop taking the supplement and consult with your healthcare provider.

The Bottom Line 

As I have mentioned in the article, human-friendly microflora may cause some unwanted side effects when consumed in certain conditions. Having proper knowledge of the side effect of probiotics, relating signs and symptoms and the mechanisms behind them as well as tips for reducing such side effects might help you avoid such undesirable adverse effects. So, It is time to apply your knowledge acquired to stay healthier than ever.

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Dr Tun Min is s GP working in NHS UK and writing articles about supplements and vitamins based on personal clinical experience and clinical research.

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