Bupropion is a medication primarily used as an antidepressant and smoking cessation aid. It is marketed as Wellbutrin and Zyban among other trade names. It is one of the most frequently prescribed antidepressants in the United States and Canada, although in many countries this is an off-label use. It is an effective antidepressant on its own, but is also popular as an add-on medication in cases of incomplete response to first-line SSRI antidepressants. Bupropion is taken in tablet form and is available only by prescription in most countries.