Antidepressant medications work by increasing levels of hormones that control mood. Selective serotonin reuptake inhibitors (SSRIs) are effective for about 5-7 out of 10 patients with depression, whereas 3-4 out of 10 see improvement with placebo alone, showing that SSRIs are nearly twice as effective. It can take SSRIs 2-4 weeks to take full effect, so patients should not stop taking them after just one week. In addition to depression, SSRIs are also used to treat anxiety, panic attacks, OCD, chronic pain, eating disorders, and PTSD. Side effects may include diarrhea, nausea, headaches, drowsiness, and sexual dysfunction.