Have you used Zyban to quit smoking?

I've used Zyban to quit smoking, actually I'm taking it now. This is my second time taking zyban, I initally stopped smoking for 2 months on 150 mg per day but unfortunately didn't get a repeat prescription , went on holiday and what with socialising , drinking, the urge to smoke came back , I have just started to take Zyban again , feeling a few side effects , but will only take 1 tablet a day and read allen carr's book , that worked for me : this medicine isn't for everyone as the side effects are a pain , but by taking the 1 tablet a day the side effects are greatly minimised. Side effects I've experienced: feeling spaced out,headaches,insomnia, constipation. Had to stop taking it initially after 4 days , then gave it another go a few days later but just stayed on 1 tablet (150mg) per day and read Allen Carr's book which in combination really helped. I have purchased Zyban with no prescription through reputable UK http://www.pharmacynextdoor.com online drugstore.