Carcinoid Syndrome Diarrhea and Serotonin

The role of serotonin in Carcinoid Syndrome diarrhea

Serotonin: More than the "happy" hormone

Serotonin is a hormone that is made and released by cells in both the brain and the gut. It's sometimes referred to as the "happy" hormone because serotonin produced in the brain helps regulate mood. But serotonin made in the gut plays an important role in other bodily functions, including bowel movements.


The brain makes 5% to 10% of serotonin in the body.
The serotonin made in the brain stays in the brain, separate from serotonin made in the gut.


The gut makes 90% to 95% of serotonin in the body.
The serotonin made in the gut can travel throughout the body in the bloodstream, but it cannot go to the brain.

Too much of a good thing

In people with Carcinoid Syndrome, serotonin levels can be greater than 5 times the average. An overproduction of serotonin by neuroendocrine tumor (NET) cells can lead to diarrhea, flushing, wheezing, fibrosis, and carcinoid heart disease among other effects.

Let's focus on one of the most common and life-disrupting symptoms of excess serotonin, Carcinoid Syndrome diarrhea. Over time, too much serotonin increases the amount of fluid in the gut. It also speeds up the function of the gut, which causes frequent, or unpredictable diarrhea. Even with somatostatin analog (SSA) treatment, some patients with Carcinoid Syndrome continue to experience diarrhea.

Controlling serotonin may mean fewer "eruptions"

You know how diarrhea can feel a bit...sudden? Kind of like when a volcano erupts? In a volcano, when too much molten rock turns into lava, it rises to the surface and erupts. In your body, excess serotonin can have the same effect. Controlling serotonin levels may be key to avoiding frequent diarrhea.