Using Bifidobacterium longum as a probiotic is generally considered safe for healthy individuals, and it typically causes only minor gastrointestinal side effects such as gas¹. However, experiencing severe feelings of depression or a flat affect can be distressing. It is possible that the changes you are feeling might be related to the probiotics, although evidence of such drastic mood changes is not commonly documented in studies about probiotics.

The symptoms you described might be due to a variety of factors:

1. Die-Off Reaction: Sometimes referred to as "Herxheimer reaction", this might happen when starting probiotics where microorganisms release toxins as they die off, potentially causing temporary symptoms such as fatigue or depression.

2. Histamine Sensitivity: If you're specifically taking a low histamine probiotic, this suggests a sensitivity to histamine, which can affect mood and energy levels.

3. Probiotic Strain Reaction: Different probiotic strains can have different effects, and not every strain agrees with every individual. It's possible that the strain, or combination of strains, you're using might not be ideal for your personal microbiome.

4. Underlying Conditions: There might be other underlying health issues at play, which could be influencing how you react to the probiotics.

Given your symptoms, it would be advisable to consult a healthcare professional who can provide personalized advice and determine whether the symptoms are related to the probiotics or another underlying cause. They might also suggest stopping the probiotic to see if your symptoms improve and help you find alternatives suited to your needs².

Footnotes

1. Office of Dietary Supplements - Probiotics ↩

2. Office of Dietary Supplements - Probiotics ↩