Happiness Drug?:

The primary idea was to inject people with cancer with bacterium that could stimulate their immune system to fight cancer tumors. But that wasn’t exactly what happened. The injection had little effect on fighting off tumors, but something else did happen. It was noticed on the patients who received this injection a mood improvement and change in life quality.

How did this come to be? They don’t know yet. Though it appears that, somehow, the bacterium, M. vaccae, triggered the patients brain cells to produce serotonin, which boosts one’s mood and well being.

There’s a possibility that this new discovery would lead to a new depression drug.

It’s pretty interesting how bacteria can lead to your happiness. But then again, anything is possible.

Source.