Zhang Yan, 33, a businessman in Changchun, Jilin Province was not self-conscious about his sexuality until an intimate chat with his friends six months ago.

Zhang (not his real name), was embarrassed when he was asked about his sexual prowess and about the length of sexual intercourse.

"I wanted to say five minutes. However, to protect my self-esteem, I told them it lasted for 10 minutes. But they still laughed at me," he told the New Culture Daily newspaper.

One of his friends suggested Viagra, the popular prescription-only pill that helps men suffering from erectile dysfunction. Instead of going to the hospital, Zhang got counterfeit pills from a sex shop.

The pills produced some encouraging results and Zhang subsequently tried various other impotence drugs over a three-month period.

Things changed suddenly when he was unable to obtain any erection.

"I was shocked and went to the hospital immediately," Zhang said. "And I later found that I had urinary tract infections, but I almost completely lost my sexual ability because I carelessly took impotence drugs."

The newspaper said many sex shops in Jilin offer fake drugs, and some shop owners claim their products could make men achieve erections for as long as 96 hours.

More than half of the 37 sex shops in Changchun approached by the newspaper sell counterfeit Viagra.

The fake Viagra cost as little as 0.3 yuan per tablet wholesale or 10 yuan ($1.4) retail.

A shop owner claimed he sells the "real" Viagra for 50 yuan ($7.3) a tablet.

The package of the so-called "real" Viagra is nearly identical to those produced by pharmaceutical company Pfizer, the creator of the drug, and the package has English labels.