Most obesity treatments suffered sales declines in the first quarter, and pharmaceutical firms attributed the poor results to a seasonal impact.

According to IQVIA, a pharmaceutical market researcher, the combined revenue of major obesity drugs slid to 7.9 billion won ($7.3 million) in the first quarter, down 8.8 percent from 8.6 billion won a year earlier.

The top seller was Ildong Pharmaceutical’s Belviq. Using lorcaserin as the main ingredient, the treatment increases satiety by activating serotonin.

Although Belviq’s revenue went down 16.4 percent to 2.4 billion won in the first quarter compared to 2.8 billion won a year earlier, it still led the obesity treatment market.

Phentermine-containing therapies followed Belviq’s lead. Daewoong Pharmaceutical’s Dietamin ranked second with 2.1 billion won sales, although the number was a 4.2 percent drop from 2.2 billion won a year earlier. Alvogen Korea’s Furimin sold 1 billion won, failing to exceed the last year’s first-quarter revenue 1.1 billion won.

On the other hand, Huons’ Hutermin saw its revenue expanding to 1.3 billion won in the first quarter, up 6.5 percent from 1.2 billion won a year earlier.

After winning approval from the U.S. Food and Drug Administration, phentermine has become a significant obesity drug in the domestic market since 2004.

Phentermine is similar in chemical structure and pharmacokinetics to amphetamine, a central nervous system stimulant. In monoamine neurons, it stimulates the secretion of norepinephrine, serotonin, and dopamine, which inhibits cognition of empty stomach. Reported adverse drug reactions include dry mouth, headache, dizziness, and sleep disorder.

Kwangdong Pharmaceutical’s Contrav, considered as the only drug to counter Belviq, had a 16.1 percent plunge in sales to 930 million won in the first quarter. In the same period of last year, it sold 1.1 billion won.

Kwangdong’s pick of Dong-A ST as a partner firm to chase Belviq with Contrav did not lead to meaningful achievement.

“Sales in winter are not as high as those in other seasons. As Belviq and Contrav were at the initial sales stage last year, their aggressive marketing work,” said an official at a drugmaker supplying an obesity treatment. “Sales (of obesity drugs) are expected to increase starting in the second quarter. As Belviq and Contrav have not been used in Korea for a long time yet, their sales will be on the rise after a certain amount of time for data accumulation.”