There are three versions of Wellbutrin, the plain (or IR), the SR, and XL.

If you're prescribed e.g. 300 mg/day of Wellbutrin, you could take 100 mg Wellbutrin IR three times a day, 150 mg Wellbutrin SR twice a day, or 300 mg Wellbutrin XL once a day.

The two extended release forms offer both convenience and more stable blood concentrations of the drug. However, the downside is that not everybody gets 12 hours out of the SR, or 24 hours out of the XL forms. Some people metabolize them faster than that, leaving them with a noticeable slump before the next dose is due.

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