A new study is challenging the long-standing theory that a lack of serotonin in the brain causes depression, as well as the value of antidepressants that are designed to address the problem.
Researchers at the University College London said evidence doesn’t support the underlying idea, originated 60 years ago, that a “chemical imbalance” in the brain produces a lack of serotonin.
That imbalance is what has long driven prescription drugs for antidepressants, known as selective serotonin-reuptake inhibitors, or SSRIs. Common examples of the drug are sertraline (Zoloft), fluoxetine (Prozac and Sarafem) and escitalopram (Lexapro).
“The serotonin theory of depression has been one of the most influential and extensively researched biological theories of the origins of depression,” researchers Joanna Moncrieff and Dr. Mark Horowitz from the college’s Division of Psychiatry wrote on opinion news site The Conversation. “Our study shows that this view is not supported by scientific evidence. It also calls into question the basis for the use of antidepressants.”
They pointed out that SSRIs are used by one in six people in England. The Centers for Disease Control and Prevention said that a little over 13% of Americans take antidepressants.
Ms. Moncrieff, a professor at the college, and Dr. Horowitz investigated the issue by conducting an umbrella review of studies into the main areas of study between serotonin and depression. Their research was published in the peer-reviewed Journal of Molecular Psychiatry.
Their review found that there was no difference in the serotonin levels of people with and without depression and that people who had depression were actually found to have higher levels of serotonin.
The researchers also assessed studies involving tens of thousands of people that looked at whether genetic factors influenced their serotonin receptors — which are what SSRIs target to take effect — to produce less serotonin.
Again, they found no distinct genetic variations in the receptors that caused people to have depression and others to not.
Ms. Moncrieff and Dr. Horowitz pointed out that some of the studies showed that people who were taking or had taken antidepressants had lower levels of serotonin.
“In fact, drug trials show that antidepressants are barely distinguishable from a placebo (dummy pill) when it comes to treating depression,” the researchers wrote. “Also, antidepressants appear to have a generalized emotion-numbing effect which may influence people’s moods, although we do not know how this effect is produced or much about it.”
The serotonin theory originated in the 1960s and gained prominence in the 1990s when the pharmaceutical industry began to market antidepressants.
The theory also earned the support of the American Psychiatric Association during that time.