Can Probiotics Cause Tiredness?

In this guide I will be explaining 3 of the biggest reasons that most people feel sluggish after taking probiotics and share what the research has to say.

If you are currently feeling sleepy after taking a probiotic, you will be relieved to know that you are not alone and it's actually quite common.

Let me explain.

Research Says Probiotics Can Make You Tired


Lady fast asleep.

When searching clinical research around probiotics you won't actually find any mentions of tiredness but I did find a study that mentioned post-prandial fatigue and weakness as symptoms which is basically the same thing.

This 2018 study from the Division of Gastroenterology/Hepatology, Department of Internal Medicine, Medical College of Georgia, Augusta University, Augusta investigated a potential link between tiredness and small intestinal bacterial overgrowth (SIBO) or D-lactic acidosis.

Researchers from the University evaluated 30 patients with Brain Fog and 8 without Brain Fog and found that patients with BF had a higher prevalence of SIBO and D-lactic acidosis, which was possibly related to probiotic use. The Brain Fog was characterized by markers related to tiredness like fatigue and drowsiness.

11% of people reported tiredness after probiotics.

As of February 5th, 2023, 4,346 people had reported side effects from Probiotic supplement usage and 479 (11.02%) of those people had self-marked Tiredness as their symptom. This data came from ehealthme a website that allows the general public to run phase IV clinical trials. Since launching my own probiotic supplement FlowFlora I haven't had any customers report anything similar but here are 3 reasons why these people might have reported these symptoms.


SIBO is a condition where an excessive amount of bacteria colonize the small intestine, which can lead to bloating, gas, diarrhea, and other gastrointestinal symptoms. Probiotics may exacerbate SIBO by introducing more bacteria into the small intestine, worsening bacterial overgrowth and causing more discomfort.

SIBO can cause tiredness due to a number of factors because when there is an overgrowth of bacteria in the small intestine, they compete with the body for nutrients, which can lead to malabsorption and nutrient deficiencies. I wrote a blog post about SIBO and probiotics recently.

The bacteria also produce gas and toxins that can cause inflammation and damage to the intestinal lining and it is this inflammation can lead to a leaky gut, allowing bacteria and toxins to enter the bloodstream and trigger an immune response.

SIBO may also interfere with the production of neurotransmitters, such as serotonin and dopamine due to the gut & brain connection which can affect mood and energy levels making you feel tired.

2) Jarisch-Herxheimer Reaction

The Jarisch-Herxheimer Reaction (JHR) is a temporary, self-limiting reaction that can occur after the start of probiotic treatment. It occurs when bacteria are killed off rapidly by probiotics, causing the release of endotoxins from the dying bacteria.

This sudden release of toxins can lead to an inflammatory response in the body, resulting in symptoms like tiredness within a few hours to a few days after starting probiotics and lasts for a few hours to a few days.

If you experience tiredness within these time frames then it may actually be a good sign and it some cases these symptoms usually go away without doing anything different at around 3 weeks of probiotic use meaning that probiotics make you feel worse before feeling better.

3) Histamine Intolerance

I have written in depth before on how some strains of probiotics can produce histamine as a byproduct of their metabolic activity. My findings were that excessive amounts of histamine can lead to histamine intolerance, which can cause a range of symptoms, including tiredness.

Some Lactobacillus and Saccharomyces boulardii strains produce a lot of histamine that can contribute to histamine intolerance by adding to the overall histamine load in the body.

If a person has leaky gut syndrome or if there is an overgrowth of harmful bacteria in the gut, this can also lead to increased histamine production, exacerbating the symptoms of histamine intolerance, including fatigue.

This third and final reason is why some individuals may feel tired after taking probiotics and may need to spend more time researching specific probiotic strains. People with histamine intolerance should avoid taking multi strain Lactobacillus & Bifidobacterium strains as this can increase the chances having histamine induced tiredness. 

Probiotics Have Never Made Me Feel Tired

I have tried pretty much every single Lactobacillus and Bifidobacterium probiotic strain already and have regularly documented my postivie and negative experiences here on my blog with various probiotic supplements.

There haven't been any strains that have made me feel fatigued or tired but the one thing I would say is that they have often helped me have a deeper sleep at night. I think this could be down to the probiotic strains working through the gut & brain axis and helping with any stress I have had during the day. 

Probiotics Do Make Other People Feel Tired

No one microbiome is the same and everyone will have different reactions to varying probiotic strains. Take some of these user reports I found for example.

2 years ago in the microbiome subreddit a Redditor called RelevantLychee said that they had experienced extreme fatigue after taking a probiotic and were looking for some advice. They had taken Renew Life Adult Probiotics 50 Billion CFU Guaranteed probiotic which is also a probiotic I have tried before. 

They explained that after taking the probiotic they have to take a nap and then they wake up feeling extremely groggy. Another Redditor explained that this sounded like a bacteria die off which is the same as a Jarisch-Herxheimer Reaction.

Another person however thought it could have been down to SIBO so it's difficult to tell in the early days of taking probiotics for the first time. My advice to this person would be to visit their Doctor first and rule out SIBO before continuing with probiotics.

Probiotics May Also Help With Tiredness

In this Reddit thread just 11-months ago another user mentioned that a Synbiotic combination of prebiotics & probiotics along with fasting had helped with their chronic fatigue. They first did a 24-hour fast before then starting probiotic supplementation which was then eventually noticed having more energy. In some follow-up comments they felt that the fast was more impactful than the probiotics.

Closing Thoughts

Probiotics can cause tiredness in some people due to various reasons such as SIBO, JHR, and histamine intolerance. SIBO can lead to malabsorption and nutrient deficiencies, and the bacteria can produce gas and toxins, leading to inflammation and damage to the intestinal lining.

The JHR occurs when probiotics kill bacteria, causing the release of endotoxins, which can lead to an inflammatory response, resulting in symptoms such as tiredness. Histamine intolerance can also cause fatigue, and some strains of probiotics can produce histamine as a byproduct.

However, probiotics can also help with tiredness in some cases, as they can work through the gut-brain axis and help with stress and heal Dysbiosis. Every person's microbiome is different, and their reactions to probiotics will vary, so it's best to consult a doctor before starting a probiotic regimen.

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