As with virtually all medication there are effects other than the ones you are taking it for. These 'side effects' do not affect everyone, but can cause problems for some people. With Zyban insomnia, dry mouth and persistent headaches are fairly common.

If Zyban is affecting your sleep you could try taking the second tablet a bit earlier on, as long as you are taking the two tablets at least 8 hours apart.

It is OK to take over the counter painkillers to help with the headaches. Some people also develop a skin rash - the recommendation is to stop using Zyban if a skin rash develops. If you are keen on continuing with Zyban, you will need to see your doctor.

Among the rarer possible effects, fits are the most serious. Because of this risk, you should not be taking Zyban if you suffer from epilepsy or have ever had any fits, no matter how minor. People who have ever had a head injury should not take Zyban either, because of the risk of seizures.