While it is actually something you should not do in general, smoking before bed has a negative effect on the body. When you smoke, your vasculature is affected and you are stimulated, which is not desirable when you are looking to calm your mind and body. In addition, smoking generally causes your heart rate to increase and blood pressure to spike. If you currently smoke, it is recommended to quit as soon as you can. Even if you have been smoking for decades, it is wise to stop as soon as possible for your health.