Today, more than 10 million people worldwide use antidepressants. The most common type blocks the reabsorption of serotonin, increasing the amount of the chemical in the brain.

Yet while depression is not a chemical imbalance, antidepressants are still prescribed to increase serotonin. The reason is not necessarily out of concern for patients; rather, the pharmaceutical industry has created a problem, sold the solution and built a billion-dollar enterprise as a result.

The scientific study of depression began around the 1960s, when researchers concluded that depression was not a disease of the soul but a problem of the brain. This came after the discovery of the neurotransmitters noradrenaline and serotonin—the “happy” chemicals released during social interaction, exercise, sunlight exposure and eating certain foods.

“The [chemical imbalance] theory wasn’t really getting anywhere,” said Joanna Moncrieff, professor of critical and social psychiatry at University College London, in a podcast interview. “But in the 1990s, when the pharmaceutical industry wanted to promote their new range of drugs for emotional problems…they picked up this theory and widely promoted it.”

Factors such as stress, early-life trauma and genetics play key roles in causing depression. While a lack of serotonin can increase vulnerability, it is not a direct cause—and it should not be treated or marketed as such.

This article is not medical advice and is not intended to encourage readers to stop taking prescribed medication. However, it is important to research what you put into your body before making a decision you may later regret.