Arena Pharmaceuticals is confident that its weight-loss drug, Belviq, will continue its upward trajectory and told investors during the first-quarter earnings call that Arena and marketing partner Eisai expect to file an extended-release version of the medication with the FDA later this year.

But the upward trend is relative. None of the recently approved prescription weight-loss medications have hit blockbuster status, despite the prevalence of obesity and the array of co-morbid conditions, such as cancer, diabetes and heart disease, with which obesity is associated, and all of them continue to court patients with financial incentives.

Arena said that that Eisai is expected to continue to support the drug’s patient savings card program, which caps out-of-pocket prescription costs at $75 per refill for patients who do not have commercial insurance coverage. It also offers $75 off to commercially covered patients after they pay a co-pay of $50 or more.

Belviq sales rose 13.7% in the first quarter of 2015, compared to the fourth quarter of last year, earning $12.8 million for Eisai and contributing $6.6 million to Arena’s $12.3 million in total quarterly sales. Arena reported a $24.29 million loss in the first quarter of 2015, compared to a $25.25 million loss for the same period last year.

Leerink Partners analyst Howard Liang wrote in a research note that Belviq accounted for 37% of total branded weight-loss prescriptions for the week of May 1, seconded by Orexigen Therapeutics’ Contrave, which accounted for 33% of branded obesity prescriptions. Vivus’s Qsymia followed with 29% of branded prescriptions for the week.

This ratio has remained similar for the three drugs over the last month. Most analysts agree that adoption of the drugs is slow.

Arena and Eisai have focused their marketing on doctors who are already high-prescribing Belviq physicians and obesity specialists. Arena CEO Jack Lief noted that the drug’s marketing is unique in that it is supported by both the neurology and contract sales forces.

Experts have attributed the slow uptake of these drugs to a variety of factors, including longstanding safety fears stemming from previous prescription medications like fen-phen and Meridia as well as costs, slow payer coverage and the need to support prescriptions for weight loss with exercise regimens and modified diets.

Yet prescriptions are slowly creeping upward. Orexigen’s partner Takeda reported $11.5 million in Contrave sales in the US for the first quarter of this year, the first full three-month period since the drug’s October launch. Orexigen executives said IMS Health trends showed patients filled 49,041 Contrave prescriptions in March, 36,387 in February and 31,765 in January. Contrave is also supported by a program that seeks to limit out-of-pocket costs for patients. The Contrave program offers a tiered program, based on coverage, with an added incentive: It knocks off an additional $10 per prescription starting with the third month’s refill. Orexigen narrowed its loss to $17.2 million during its most recent quarter, compared to the $24.9 million net loss it reported during the first three months of last year.

Vivus, which has marketed Qsymia without a partner since receiving the FDA’s approval three years ago, is also seeing slow progress in sales.

The firm announced in March that it would instead focus its sales force on “the most productive target areas,” such as payers, and it would increase its digital profile through efforts like search engine optimization and “other Web-based patient outreach.”

Qsymia had $12.6 million in sales for the first quarter of this year, compared to $9.1 million in the same period in 2014. The company spent $18 million marketing Qsymia during the first quarter, compared to $18.7 million during the same period last year. Vivus attributed the smaller promotional spend to “more focused spending on our marketing and promotional programs.”