Bupropion (Aplenzin, Wellbutrin, Wellbutrin SR, Wellbutrin XL) is used to treat depression. Bupropion (Aplenzin, Wellbutrin XL) is also used to treat seasonal affective disorder (SAD; episodes of depression that occur at the same time each year [usually in the fall and winter but rarely may occur in the spring or summer months]). Bupropion (Zyban) is used to help people stop smoking. Bupropion is in a class of medications called antidepressants. It works by increasing certain types of activity in the brain.
Bupropion comes as a tablet and a sustained-release or extended-release (long-acting) tablet to take by mouth. The regular tablet (Wellbutrin) is usually taken three times a day, with doses at least 6 hours apart, or four times a day, with doses at least 4 hours apart. The sustained-release tablet (Wellbutrin SR, Zyban) is usually taken twice a day, with doses at least 8 hours apart. The extended-release tablet (Aplenzin, Wellbutrin XL) is usually taken once daily in the morning; doses of the extended-release tablet should be taken at least 24 hours apart. When bupropion is used to treat seasonal affective disorder, it is usually taken once a day in the morning beginning in the early fall, continuing through the winter, and stopping in the early spring. Sometimes a lower dose of bupropion is taken for 2 weeks before the medication is stopped. Take bupropion with food if the medication upsets your stomach. If you have trouble falling asleep or staying asleep, do not take bupropion too close to bedtime. Take bupropion at around the same time(s) every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take bupropion exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.
Summary from MedlinePlus.gov, click for more information.