I can only add my anecdotal story here.

I recently had mouth surgery where they had to open up the lower part to access the jaw bones. From what I understand, they sterilize your mouth pretty well beforehand. I had to rinse my mouth out with a foul tasting mouthwash and woke up with strange tastes and dark products around my lips. Since then, I've felt like crap. At first I thought it was the surgery itself. Then a long effect of the anesthesia. Except that it did not go away.

Anyway, I recently read a lot about probiotics and decided to try L. reuteri orally.

The result is so instantaneous that I was scared it might be psychosomatic from a placebo. But if it is indeed a placebo, it is the strongest I have experienced, so I doubt it.

My mouth went from always dry and smelly to well hydrated in one day. After 5 days, my mood completely changed, including the quality of my sleep.

I don't know if I was depressed per se, I had not consulted anyone. However, I had a heavy weight on my shoulders that is now gone.

Since that experience, I have added L. reuteri pills made for gut health to my diet. I am now considering making my own probiotic yogurts and as a family we have started to experiment with fermented sauces and pickled vegetables.

There is something very important about probiotics that is almost overlooked. I think we should all pay much more attention to it.