Cigarettes

Cigarettes affect your entire body in a negative way. Eight seconds after you inhale cigarette smoke, nicotine (the chief active principle of tobacco) reaches your brain and stimulates pleasure centers. You like the feeling, so you smoke again. Your body eventually builds up a tolerance for tobacco and you need more to get the good feeling. Eventually, you realize how much you're harming your body and you decide to quit. But not smoking gives you headaches and makes you grouchy, restless, depressed and hungry. You're addicted, and the chances that you'll be able to quit are only one in 10, according to the National Institute on Drug Abuse.