What is the primary reason a patient would be prescribed this medicine?

What is the medication of choice?  i.e.  Zoloft

• What is the primary reason a patient would be prescribed this medicine?  i.e. depression
• What is the medication’s mechanism of action?  i.e.  How does this medicine work?
• What are the five most common side effects of the drug? i.e. nausea, drowsiness
• How are these side effects the result of the drug? i.e. Is this drug interacting with chemicals that contribute to nausea, drowsiness?   What is chemically making me drowsy?