A Chinese court has upheld Viagra-maker Pfizer's patent for the anti-impotence pill, overturning a previous decision.
The majority of Viagra pills sold in China are not made by Pfizer
Most drugs sold as Viagra in China are counterfeit, and the ruling shows the country is prepared to get tougher on intellectual property rights violation.
In 2004, China's patent review board sided with Chinese generic drug makers challenging Pfizer's sildenafil citrate patent, Viagra's main ingredient.
New York-based Pfizer recorded Viagra sales of $1.65bn (£0.87bn) in 2005.
An official at the Beijing No 1 Intermediate People's Court confirmed the decision.
Pfizer had appealed to China's State Intellectual Property Office(Sipo) over the 2004 decision by the patent review board permitting more than a dozen Chinese drug firms to use sildenafil citrate.
Viagra was introduced in China six years ago and after six months on the market, state media said 90% of the blue pills sold in Shanghai were fake.
Viagra is known locally as "weige" or "great brother" in Chinese.
The local producers, known as the "Weige Alliance", are expected to appeal against the latest decision.
"We respect the Chinese law and the decision made by the court. But we may appeal," said Qing Liang, a spokesman for Guangzhou Baiyunshan Pharmaceutical, a firm looking to market a generic version of Viagra.
When it joined the World Trade Organization in 2001, China agreed to tighten patent protections.