Depression May Not Be Associated With Low Serotonin Levels, New Research Review Suggests

There is so much nuance (and frankly, confusion) when it comes to mental health—still, experts are continuing to uncover new insights, to shed some light on this complex topic.

Still, despite the influential scope of this theory, "no comprehensive review has yet synthesised the relevant evidence," the researchers share. That is, until now.

Based on data from 17 different studies on serotonin, the researchers found "there is no convincing evidence that depression is associated with, or caused by, lower serotonin concentrations or activity."

The authors went on to state, “Most studies found no evidence of reduced serotonin activity in people with depression compared to people without, and methods to reduce serotonin availability using tryptophan depletion do not consistently lower mood in volunteers."

It's worth noting that in some studies, there was minor evidence that pointed toward a tie between increased serotonin activity and depression, but the researchers believe these results were likely "influenced by prior use of antidepressants and its effects on the serotonin system."

If depression is not, in fact, caused by low levels of serotonin, this also calls into question the efficacy of antidepressant medications.

The review reveals that there is evidence that people who are taking antidepressants may actually have lower levels of serotonin in their blood, contrary to the intention. "These findings suggest that in the long-term antidepressants might produce compensatory changes that are opposite to their acute effects," the authors note.

As for individuals who have benefited from this type of medication, the review posits, "Other explanations for the effects of antidepressants have been put forward, however, including the idea that they work via an amplified placebo effect or through their ability to restrict or blunt emotions in general."