Cigarettes are addictive because of the nicotine in them. Nicotine is a HIGHLY addictive substance that can be found in tobacco. It causes stress relief to your brain and can elevate your heart rate. After your body has had even the slightest bit of nicotine it will feel like you need more. So basically nicotine is and the temporary feeling of stress being relieved gets you addicted.
Hope this helps!! :D
