Nicotine
"I'm a young male 26 years old.  Was a casual smoker for 7 years. Started very young at 16. Became a pack a day smoker for 3  years.  So more than 10 years of smoking.  Other reviewers are spot on about insane irritation/itching when patch is first applied to skin. This lasts for the first 20 minutes.  Do not let this deter you , try not to think about it. I'm on the 21mg patch.  This is recommended for smokers who smoke at least a pack a day or more. I can honestly say you really have to be determined to stop smoking altogether.  Side note. Was a very heavy cannabis smoker as well, and remarkably the patch has also gotten rid of all cravings for cannabis as well. If you're serious about kicking this filthy habit this patch works wonders ."