Can Probiotics make you Tired?

Tired female entrepreneur yawning in office. Horizontal shot.
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Nothing we ever do is exempt from consequence. There are pros and cons to many things in life and that includes Probiotics.  Thus, we always need to decide and be able to balance how good and bad a given choice is. The same thing is true for synthetic drugs; a more natural approach to medicine has its safety concerns and considerations. However, what can we say about probiotics? Do they make you tired?

The jury is out in the scientific coumminty  whether fatigue, tiredness and brain fog are attributible to Probioitcs making a person tired. There is some evidence that D-Lactate is responsible in some Probioitcs for tiredness or brain-fog, but its still not entirely a clear-cut finding.

In the market, we can see how the use of these supplements is booming sky high, and they don’t need a prescription. But it would be wise to understand the possible side effects of probiotic therapy before starting to use them in our day-to-day. One of the reported side effects is that probiotics can make you feel tired, but is that true?

Safety considerations using Probiotics!

Probiotics are excellent therapeutic tools with an impressive potential to improve many different conditions. They are widely used in the medical field to improve cases of chronic diarrhea, and they have been found useful as a side treatment for other gastrointestinal ailments as well as autoimmune problems, and much more.

However, the responsible use of probiotics should also consider the side effects of this revolutionary method. Thus, patients may experience the following symptoms after using probiotics:

  • Bloating and abdominal cramps: The intestinal bacteria included in probiotics will grow in your intestinal lumen and start creating gas. Thus, you may feel bloating and sporadic abdominal cramps.
  • Nausea and taste disturbances: Some patients have reported nausea, but it is quite uncommon. However, taste disturbances are apparently more common, and they are possibly due to a modulation of the nervous system in the gastrointestinal tract.
  • Low appetite: Similarly, you may find a reduction in your appetite levels caused by chemical modifications in the gastrointestinal tract that may be used in our advantage to favor weight loss.

There are also sporadic cases of bacteremia, sepsis, and other health problems presumably caused by probiotics use in immunocompromised and terminal patients. For this reason, if you are hospitalized or have a serious disease it is a good idea to talk to your doctor before starting probiotics.

However, recent studies have mentioned brain fogginess and chronic fatigue as possible side effects of probiotics, and there’s an ongoing debate in the scientific community about whether or not they are caused by these microorganisms.

Can probiotics make you feel tired?

In the scientific community, the discussion about whether or not probiotics can make you feel tired started in June 2018. This year, a paper was published in the journal Clinical and Translational Gastroenterology describing patients who received probiotic treatment and went through a condition called Small Intestinal Bacterial Overgrowth (SIBO) and D-Lactic acidosis. These conditions led to brain fogginess in these patients, which feels pretty much the same as tiredness and fatigue.

Brain Fogginess and Tiredness Probiotic Research

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D-Lactate was reported to be behind these findings. It is a molecule synthesized by certain bacteria as a result of fermentation, and unlike L-Lactate (which is produced by the human body), this variant of lactate is not quickly metabolized by the liver. Thus, when produced massively by these bacteria, it is likely to be accumulated.

The thing about D-Lactate accumulation in the body is that this is lactic acid, and increases the acidity in the blood and the tissues. After a while, D-Lactic acidosis reaches the brain and blocks nerve connections in the brain, causing the sensation of brain fog and making patients feel tired.

However, as mentioned before, there is an ongoing debate, and this is not the only scientific article covering the topic. As we will see further, other authors are against the notion that probiotics will cause D-Lactic acidosis, and have criticized and commented upon the findings of the study published in 2018.

D-Lactate and brain fogginess. Are probiotics involved?

In the same year and the same journal, a debate followed about whether or not probiotics are involved in D-Lactate acidosis and brain fogginess. In their article “‘Brain Fogginess’ and D-Lactic Acidosis: Probiotics Are Not the Cause,” Quigley and colleagues mention the following arguments in defense of probiotics:

  • The authors are joining probiotic use with small intestinal bacterial overgrowth, two separate entities that should be evaluated independently if we want to show accurate results.
  • There are serious methodologic problems with the paper because the patients were diagnosed with SIBO (a condition that produces many metabolites that lead to brain fogginess, not just D-Lactate), and probiotics were not the only therapy used during the evaluation. It was not a randomized, double-blind study, either.
  • The majority of Lactobacilli and all Bifidobacteria species produce the same L-Lactate humans can metabolize. They do not produce D-Lactate and cannot be blamed for any D-Lactate increase.
  • D-Lactic acidosis can be actually treated using probiotics and choosing bacterial strains that do not produce D-Lactate. Thus, incriminating probiotics is misleading and inaccurate.

This criticism was followed by another article as a response, where the authors of the original paper mention that they found evidence of SIBO through breath tests and duodenal aspirates in 68% of patients using probiotics against 28% of those who did not consume this treatment. Among other counterarguments, they mention that their study was not meant to address which probiotic strain is responsible but to understand the origin of debilitating symptoms that probiotics may trigger.

Can I stop my Tiredness?

The neurologic symptoms, and it is important to understand whether or not probiotics create a chemical or neurologic alteration that may be responsible for making you tired because this may have more significant implications in susceptible patients. Thus, there is an ongoing debate in the scientific community about whether or not probiotics are the real cause of these symptoms.

D-Lactate is a candidate to understand the association between probiotics and brain fogginess. This variant of lactic acid is metabolized very slowly in the human body and tends to accumulate, but not every probiotic strain creates D-Lactate, and the evidence presented so far is not enough to incriminate probiotics as a whole or a given strain of probiotics as a cause of fatigue and brain fog resulting from D-Lactate acidosis.


Lerner, A., Shoenfeld, Y., & Matthias, T. (2019). Probiotics: If It Does Not Help It Does Not Do Any Harm. Really?. Microorganisms, 7(4), 104.

Reid, G., & Dhir, R. (2019). Probiotics: Reiterating what they are and what they are not. Frontiers in Microbiology, 10, 424.

Rao, S. S., Rehman, A., Yu, S., & De Andino, N. M. (2018). Brain fogginess, gas and bloating: a link between SIBO, probiotics and metabolic acidosis. Clinical and translational gastroenterology, 9(6), 162.

Quigley, E. M., Pot, B., & Sanders, M. E. (2018). ‘Brain Fogginess’ and D-Lactic Acidosis: Probiotics Are Not the Cause. Clinical and translational gastroenterology, 9(9), 187.

Sachdeva, S., Puri, A. S., Kumar, A., Dalal, A., & Dahale, A. S. (2018). Brain Fogginess and SIBO: A Link or Just a Mirage?. Clinical and translational gastroenterology, 9(9), 184.

Rao, S. S., Yu, S., Tetangco, E. P., & Yan, Y. (2018). Probiotics can Cause D-Lactic Acidosis and Brain Fogginess: Reply to Quigley et al. Clinical and translational gastroenterology, 9(11), 207.

About Simon Bendini 55 Articles
Hello, I'm an expert in all things Probiotics. I also live and breathe what I write about: I take Probioitcs EVERY day. I want to help you discover the benefits of them too. Enjoy my humble site.

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