Antidepressants are a class of medication used to treat depression. Different antidepressants work on different neurotransmitters, which receive different chemicals that affect mood. Lexapro, Prozac and Zoloft are medications known as SSRIs (Selective Serotonin Re-Uptake Inhibitors) and prevent the chemical Serotonin from being broken down too quickly. Wellbutrin works on the neurotransmitter handling norepinephrine. Medications such as Effexor, Pristiq and Cymbalta target both norepinephrine and serotonin. Antidepressants are not addicting in any way and you cannot become chemically dependent upon them. However, it is unwise to stop antidepressants abruptly as you can experience withdrawal-like symptoms (known as discontinuance symptoms) due to your body having gotten used to the medication.
She has depression, so her doctor prescribed antidepressants.