Thanks largely to the introduction of a hefty cigarette tax in Japan this fall, the world’s largest pharmaceutical company is scrambling to meet surging demand for a controversial drug for quitting smoking.

Japanese smokers are begging for Pfizer’s Chantix or, as it is known there, Champix — a pill that works by altering the way nicotine typically affects the brain and which, after a major ad campaign, is widely seen as the No. 1 stop smoking aid, The New York Times reports.

In October, the government approved a tax hike that forced nicotine addicts to pay more than 400 yen for a pack of 20 cigarettes, instead of the 300 yen, or about $3.60, they’ve been accustomed to paying. The new price tag converted many smokers into would-be quitters, yet Pfizer seems to have been caught off guard, struggling to produce enough of the medication.

“After all that advertising, it turns out they don’t have enough,” said Hiroya Kumamaru, director of the KI Akihabara Clinic in Tokyo, which is turning away patients seeking the medication. “They should have predicted something like this.”

Pfizer appears to have missed an important opportunity, especially since sales of the drug have lagged in the U.S. As FairWarning reported in December, safety concerns–including reports of suicides, attempted suicides and psychosis–have plagued the drug ever since it was approved by the Food and Drug Administration in 2006.

According to The Times, while revenue from Chantix fell 17 percent in the United States to $252 million in the first nine months of 2010, sales in the rest of the world grew 22 percent to $270 million.

Pfizer says it underestimated how much demand would grow for the drug in Japan but promises patients will soon have access to the medication.

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