https://www.vice.com/en_us/article/88qge4/the-new-study-on-serotonin-and-depression-isnt-about-antidepressants-chemical-imbalance

In the original TV ad for the antidepressant Zoloft, a gray cloud hovers over a sad blob, rain falling on the blob’s dejected expression. “You know when you feel the weight of sadness,” a voiceover says. 

The commercial lists the symptoms of depression, and explains that “while the cause is unknown, depression may be related to an imbalance of natural chemicals between nerve cells in the brain. Zoloft works to correct this imbalance. You shouldn’t have to feel this way anymore.”