The growth of erectile dysfunction medicines is slowing, with the sales of impotence drugs remaining stagnant and original treatments suffering a rapid sales decline.

According to data from IQVIA, the combined sales of erectile dysfunction drugs fell to 57.7 billion won ($51.5 million) in the first half of this year, down 3.6 percent from 59.8 billion won a year earlier.

Original blockbuster Viagra by Pfizer and its competitor Cialis by Lilly had the steepest drops in sales, and most of the other medicines also performed poorly.

Hanmi Pharmaceutical’s Viagra copy Palpal topped the sales with 17.1 billion won in the first half, although the number fell short of the 17.8 billion won revenue recorded a year earlier. It was the only treatment that sold more than 10 billion won in the first half among impotence drugs.

Hanmi’s Gugu, an imitation of Cialis, enjoyed a revenue growth. Gugu sold 7 billion won in the first half, up 3.1 percent from 6.8 billion won a year earlier.

Chong Kun Dang’s tadalafil Cendom marked an 8.1 percent decline in sales from 6.3 billion won to 5.8 billion won during the same period. Despite Cendom’s underperformance, Chong Kun Dang expanded lineups of impotence medicines. After Chong Kun Dang released sildenafil-containing Cengla in the second half of last year, the treatment sold 1.1 billion won in the first half.

With Cengla in the market, Chong Kun Dang sells both tadalafil and sildenafil drugs, the two representative agents in the erectile dysfunction treatment market.

The original drug Viagra ranked fourth in sales. Viagra’s revenue fell 9.9 percent year-on-year to 5.2 billion won in the first half from 5.7 billion won a year earlier.

Cialis, which used to lead the market after Viagra’s patent expiration, is struggling as well. Cialis sales plunged 31.7 percent to 3.6 billion won in the first half from 5.3 billion won a year earlier, which was the most significant revenue drop among leading products.

Dongkoo Bio Pharm’s Zygra, which is showing strong performance in the urology market, sold 976 million won, rising 9.7 percent year-on-year in the cited period. If it maintains the growth momentum, its sales are likely to reach 1 billion won.

Hanmi’s Gugutams, the first combo drug mixing enlarged prostate treatment tamsulosin and impotence drug tadalafil, showed a growth potential by selling 1.3 billion won in the first half.

“The erectile dysfunction treatment market has almost reached maturity. What we have to watch now is how new products will perform,” said an official at a pharmaceutical company. “Market shares will change according to how much Gugutams will carve out its market share and how Chong Kun Dang, which also released sildenafil, will enhance its sales power.”