The obesity drug battle was the most hotly contested pipeline race last year. But the sluggish initial sales of VIVUS' (NASDAQ:VVUS) Qsymia revealed the tricky nature of the weight loss market. Now Arena Pharmaceuticals (NASDAQ:ARNA) is gearing up to launch Belviq, which was approved first but held up in regulatory procedures.

Does Belviq stand a better chance at the blockbuster status that fueled investment dreams?

Launch details
Belviq was delayed by Drug Enforcement Agency scheduling -- a process that's nearly complete.

DEA scheduling involves several steps and can be lengthy. A proposed schedule IV designation for Belviq appeared in the Federal Register on Dec. 19, and a 30-day public comment period followed. The DEA takes these comments into consideration before finalizing the designation. While this process nears completion, Arena and partner Eisai are getting Belviq ready to go. In their most recent earnings call, Arena estimated that Belviq would hit the U.S. market in the first quarter of this year.

What will the launch mean to the Arena-Eisai deal financials?  

Arena will have received around $150 million in payments from Eisai prior to launch, which includes $65 million following the DEA scheduling. The post-market agreement has Arena selling the product to Eisai for a percentage of net sales, with that percentage increasing from 31.5% to 36.5% depending on the amount of sales. Arena can receive an additional $1.2 billion as a purchase price adjustment.

Initial sales prediction
Predicting this market falls into the category of fool's (small "f") errand.

I've previously mentioned that it wouldn't matter which drug was first out of the gate. The prescribing instructions for both Belviq and Qsymia advise patients to discontinue treatment if a certain percentage of weight loss isn't achieved within 12 weeks.

Belviq will have an easier time getting to patients, but that's partly because of timing. Insurers already started coming aboard for Qsymia, and prescription rates grew. Belviq has a sales advantage since it lacks the Risk Evaluation and Mitigation Strategy  Qsymia was assigned, which restricted Qsymia to mail-order pharmacies.

Don't forget...
Orexigen (NASDAQ: OREX) is still on deck with its leading obesity drug Contrave. Approval depends heavily on the Light Study cardiovascular light safety trial. But the FDA's willingness to accept those results after the review begins is another sign of the agency lightening up on obesity treatments.

Foolish final thoughts
There are three certain things in life: death, taxes, and investor arguments over which obesity drug will win. Patients will likely take time in finding the treatment that works the best based on individual needs. If the Qsymia launch taught us any lesson, it's that this market will define itself over time.