By Adrienne Dellwo Updated on April 10, 2021
Medically reviewed by David Ozeri, MD

We hear a lot about low serotonin in fibromyalgia (FMS) and chronic fatigue syndrome (ME/CFS), and it's usually in relation to its function as a neurotransmitter (chemical messenger in the brain.) However, serotonin is also busy all over the rest of your body as a hormone. Body-wide serotonin dysregulation is believed to be a part of these conditions as well, and it might contribute to many of our symptoms and overlapping conditions.

The name serotonin is related to serum, which is a component of blood. That's because it's earliest known function was narrowing the blood vessels. Researchers have noted irregularities with blood flow in both of these conditions:

  • In FMS, research shows abnormal blood-flow patterns in the brain, with more than normal in some areas and less than normal in others. We don't know the specific effects of this, but researchers do know that blood flow has a significant impact on brain function.
  • Also in FMS, some researchers theorize that the horrible burning pains we get are due to ischemia (impaired blood flow), which basically means the area "falls asleep" and then gets those painful pins and needles as the blood, and therefore feeling, returns.
  • In ME/CFS and to a lesser degree in FMS, some research has shown low blood volume, which results in cells that are starving for oxygen and nutrients. Picture being at a high altitude and struggling to catch your breath. Now imagine that you also haven't eaten all day. That's what every cell in your body may be going through.

At this point, we don't have research on the possible relationship between serotonin dysfunction and these specific irregularities, but it's certainly a connection that seems logical.

The relationship of serotonin to fibromyalgia isn't fully understood but appears to be fairly straightforward. Not so for ME/CFS. This is one area where we have to look at the conditions separately.