Researchers at the Washington University School of Medicine in St. Louis recently found that a connection between serotonin and depression, long taken as gospel, does not actually exist. The research disproved a landmark 2003 study, which has since been cited more than 4,000 times, that linked the serotonin gene to inhibited ability to deal with stress and, in turn, a greater likelihood of depression.

By analyzing information from more than 40,000 people in more than 100 studies that have been done since 2003, the researchers found that the gene likely does not alter the impact stress has on depression.

Read: Half Of All College Students Stressed, Too Poor To Eat

The results, published last week in the journal Molecular Psychology, put an end to the two-decade-long debate about stress and serotonin genes.

“Experts have been arguing about this for years. But ultimately, the question has to be not what the experts think but what the evidence tells us,” Robert C. Culverhouse, professor of medicine and biostatistics and the study’s lead author, said in a press release from the university. “We’re convinced the evidence finally has given us an answer: This serotonin gene does not have a substantial impact on depression, either directly or by modifying the relationship between stress and depression.”

Depression is one of the most common mental health disorders in the U.S., so rooting out its cause has remained a high priority for researchers. More than 7 percent of people 12 years of age or older suffer from depression in the U.S., according to the Centers for Disease Control and Prevention.

Read: Cortisol Hormone In Hair Can Diagnose Stress And Depression Without Blood Test

“The idea that differences in the serotonin gene could make people more prone to depression when stressed was a very reasonable hypothesis,” Laura Jean Bierut, Alumni Endower Professor of Psychiatry at Washington University, said in the press release. “But when all of the groups came together and looked at the data the same way, we came to a consensus. We still know that stress is related to depression, and we know that genetics is related to depression,  but we now know that this particular gene is not.”