I will be interested to see which drug doctors and patients turn to first. Will it be Qnexa, with its promise of faster and greater weight loss despite some safety and tolerability issues? Or will Belviq be used first -- safer despite lackluster weight loss? Obese patients may try both drugs eventually, if they can afford the high out-of-pocket costs since reimbursement is going to be hard to come by at first. The Japanese drug maker Eisai will be selling Belviq in the U.S. on behalf of Arena. Eisai's biggest commercial success here has been the Alzheimer's drug Aricept although most of the marketing responsibilities and credit goes to Pfizer, which co-promoted the drug. The jury is still very much out on whether Eisai can succeed with Belviq. Vivus has no U.S. marketing partner for Qnexa, but will field its own 250-person sales force to sell the drug to doctors who specialize in obesity. Vivus will also distribute Qnexa via mail-order pharmacy only, unlike Belviq's availability in retail pharmacies. Vivus says mail-order distribution is convenient and shouldn't hamper Qnexa's commercial roll out. That sounds like wishful thinking. Thomas E. asks, "You doubt the writer's prediction that Belviq can become a $10 billion drug, even with one-third of Americans diagnosed with obesity?" Yes, I have my doubts. Thomas is referring to a column published by Seeking Alpha in which a pseudonymous Arena investor forecasts Belviq sales of $10 billion. Here's what he wrote: "I forecast 250K scripts in the first full quarter of launch and for Belviq to generate over $1B in revenue in the first 6 months from launch, $2-3B in 2013 and to reach $10B in annual sales by 2015. Yes, these are audacious numbers unless you are open to looking at the size of the market without consideration of performance of previous weight loss drugs. There is no bigger market in all of pharma, with over 100M prospective patients in the US alone. There has never been a safe option for physicians to try. There is tremendous pent-up demand for options from both prescribers and patients." Reality check: Vertex Pharmaceuticals' hepatitis C drug Incivek is the only drug I'm aware of that reached $1 billion in cumulative sales after just six months on the market. Incivek cures hepatitis C. Arena's Belviq cures nothing and doesn't really help people lose much weight. Belviq will be launched in early 2013, yet this author believes Belviq will generate over $1 billion in sales by next June, then double sales by December 2013. Really? If Belviq somehow achieved $10 billion in sales at any time, it would be only the second drug in history to do so. The first and only $10 billion drug was Pfizer's Lipitor. Three other drugs -- Plavix, Seretide/Advair and Humira, have come close, according to EvaluatePharma. A word of advice to Arena diehards: Lower your expectations.