The Biotech Mailbag is open. My column on Arena Pharmaceuticals ( ARNA) and the looming release of phase III data on it's obesity drug lorcaserin seemed to hit a nerve with some die-hard Arena fans. Several people emailed to say I was too bearish and that I should not have quoted Canaccord Adams' analyst Adam Cutler, who downgraded the stock recently. The flurry of Arena-focused email included (naturally) the tired claim that I was trying to drive down the Arena's stock price purposely at the bidding of my hedge fund overlords. I stand by the column. It was a realistic look at the challenges Arena faces. Obesity drug development is fraught with risk, and the current drugs in development -- Arena's lorcaserin or the competing drugs from Vivus ( VVUS) and Orexigen Therapeutics ( OREX) -- haven't exactly inspired much confidence yet. Yes, Arena has engineered lorcaserin to avoid the cardiovascular toxicities seen with its chemical cousin fenfluramine, but at the same time, potential central nervous system side effects remain an under-appreciated risk. Also under-appreciated by a lot of investors is how skittish regulators at the FDA and their counterparts in Europe are about the risk-benefit of any weight-loss drug. The bar for approval in this indication is going to be very high given all the safety missteps of the past. Fat Americans are screaming for a pill that will help make muffin tops and beer guts disappear, but the FDA -- and ultimately the insurance companies who will be asked to pay for the drugs -- may not be as eager to deliver.