NEW YORK (CNN/Money) - Pfizer Inc. Tuesday unveiled an experimental drug to help people quit smoking that could become the drugmaker's next blockbuster.

Shares of Pfizer (PFE: Research, Estimates), the world's largest drugmaker, jumped about 4.6 percent on the news, which was released as Pfizer gave fresh details on its pipeline of experimental drugs at an investor conference here.

In clinical trials involving several hundred smokers, the New York-based company said almost half of smokers given this oral medicine, called Varenicline, were able to quit smoking after only seven weeks.

In the same trial, only 16 percent of people receiving sugar pills managed to stop, while 33 percent of patients who received Zyban, a pill made by GlaxoSmithKline (GSK: Research, Estimates) and also sold as Wellbutrin for depression, were able to quit, the drugmaker told CNN/Money.

"This is a significant improvement over results achieved with Zyban, an antidepressant approved as an aid to smoking cessation," said Joe Feczko, president for worldwide drug development at Pfizer.

Side effects of the Pfizer drug appeared negligible so far, and the drug has "an excellent safety profile," said Betsy Raymond, Pfizer's spokeswoman.

Varenicline is currently in the final phase of widespread human clinical trials, but there's no timeline for when the anti-smoking drug might hit the U.S. market, she added.

Pfizer also declined to predict when Varenicline could win approval from regulators in other countries.

The company, however, cautioned that the results of its big clinical studies will take time, and a positive outcome isn't always guaranteed.

Pfizer's new drug was inspired by a natural remedy tested by doctors in the Soviet Union in the late 1960s. The Soviet doctors had tested a chemical called cytisine, derived from a weed sometimes called false tobacco, as a pill to help smokers kick the habit. They reported that cytisine partially activated the nicotine receptors in the brain without being addictive.

Nearly three-quarters of America's 50 million smokers try to quit smoking, according the Wall Street Journal. But their rate of success is low.

Pfizer said it is unclear how long patients need to be on Varenicline after quitting.

The company also said it expects annual earnings to rise 16 percent this year and next, boosted by cost cuts from its $60 billion acquisition of Pharmacia Corp. and by increased sales of key medicines.

The drugmaker's best-selling products include anti-impotence drug Viagra and cholesterol drug Lipitor.