Zydus Cadila, one of India’s largest drug makers, said it has received tentative approval to market tadalafil, the generic ingredient of the most popular erectile dysfunction drug Cialis, in the US market.

The drug will be manufactured at the group’s facility at Moraiya, Ahmedabad.

The USFDA approval comes weeks before Cialis is expected to lose patent protection, in September this year.

Generic drug makers almost started selling tadalafil tablets in the US last year after Adcirca, a hypertension drug also manufactured by Eli Lilly, moved out of patent protection in November. Adcirca too is made from tadalafil.

The move was opposed by Eli Lilly, which argued that it had protection till 2020 on Cialis, which was also made out of tadalafil.

However, Eli Lilly and generic manufacturers reached an agreement under which Eli Lilly was permitted to hold on to market exclusivity till September 27 this year.

It is expected that generic drugmakers could start selling tadalafil tablets in the US from Sep 28.

Cialis is the most popular erectile dysfunction drug in the US, with sales of around  $2.5 bln per year in the country.

However, it is facing tough competition after patent expiry on its main competitor, Viagra, expired in December last year.

Because of patent expiry, cheaper versions of Viagra have filled the US market, driving down sales of Cialis. It is believed that tadalafil will recapture much of the market once generic players enter the market in September.