It is important that you take Zyban according to the patient directions that you get from your pharmacy to minimize any chances of side-effects. Your doctor will likely prescribe Zyban at 150mg strength to be used once a day for the first three days. Then on the fourth day, you will likely be told to increase the dose to 300mg per day - one 150mg pill in the am and the second 150mg pill in the pm. It is very important to take the doses at least 8 hours apart. You should never take both pills at the same time as this can increase your chances of side-effects. Some people continue on one pill a day and do very well. Talk to your doctor.
Source: (1)'Zyban (buproprion hydrochloride) Sustained Release Tablets Prescribing Information. GlaxoSmithKline, Research Triangle Park, NC. 3/2003.