The leading anti-smoking drug by far is Chantix from Pfizer (PFE), which generated more than $700 million in sales in 2011. 

Approved in 2006, Chantix is the only branded treatment on the market. However, it's not without issues. Its effectiveness is considered moderate, and a recent analysis of clinical trials showed a higher rate of heart attacks or strokes in patients using Chantix than those who didn't take the product.

A second anti-smoking drug is Zyban from GlaxoSmithKline (GSK). It's actually the antidepressant Wellbutrin repackaged as a smoking cessation aid. Zyban has been available as a generic since 2004 and combined sales are estimated to be in the $20 million to $25 million range annually. 
 
We all know that quitting smoking is harder than hitting a three-point basket from behind mid-court blindfolded with one hand tied behind your back. You can thank the addictive power of nicotine for that. Most people just can't cope with the symptoms that go along with quitting smoking: dizziness, depression, irritability, and sleep disturbances, to name a few. So it's no surprise that of the multitude of smokers who want to quit every year, only a tiny percentage succeed, and those mostly do so on willpower alone.
 
Many people turn to over-the-counter patches, inhalers, gums, and lozenges for their nicotine fix, hoping these substitutes can help wean them away from cigarettes. These alternatives are far from ideal because the risk is high that while users may quit smoking, they will become dependent on the replacement product -– and the risk of relapse is also high. Still, these products are considered attractive inasmuch as they don't contain the tars and toxins of tobacco smoke.
 
Many smokers were counting on the development of vaccines that could produce antibodies against nicotine, heading it off before it reaches the blood–brain barrier. The trailblazer candidate was NicVAX, for which Glaxo paid $40 million for worldwide marketing rights. Unfortunately, the vaccine didn't achieve good results in a Phase 3 trial.
 
For the company that does develop an effective anti-smoking drug, the potential payoff could be huge. It's estimated there are 1.3 billion smokers worldwide and about half of them want to quit. China alone has 300 million smokers.