The most commonly prescribed antidepressants, known as SSRIs and SNRIs, affect the brain chemicals serotonin or both serotonin and norepinephrine, respectively. Your doctor considers side effects, safety, tolerability, and your history of depression when prescribing antidepressants. You may experience mild to severe side effects like dry mouth, nausea, insomnia, sexual problems, changes in blood pressure, or suicidal thoughts from antidepressants. Sometimes side effects go away. If severe side effects persist, talk to your doctor about changing medicines.