Ironwood Pharmaceuticals (Nasdaq: IRWD) Linzess got the early FDA approvals flowing this week.

Yesterday, the biotech announced that the FDA had approved Linzess, its treatment for irritable bowel syndrome. The PDUFA date for the drug wasn't until Sep. 8. Of course, the FDA took an extra three months to review some additional data it requested; so, perhaps finishing early, especially right before a three-day weekend, shouldn't be all that surprising.

Ironwood and partner Forest Labs (NYSE: FRX) plan to launch the drug in Dec., after the companies get feedback from the FDA on their promotional materials. The holiday season seems like an inopportune time to launch a drug, but Forest said it's had good results with launching around that time of the year. Perhaps "get a better drug to treat my IBD" will be on some people's New Year's resolution list.

The key for a quick launch is to capture patients who are dissatisfied with current treatments. Ironwood and Forest think there are potentially 10 million patients that fit into that category.

Most patients are taking over-the-counter medications, like Procter & Gamble's (NYSE: PG) Metamucil or Novartis' (NYSE: NVS) ex-lax. In theory, converting OTC patients to prescription patients is difficult, because it's more convenient to try something else on the pharmacy shelf than head to the doctor's office. But Ironwood thinks these patients are so desperate to find something that works, that they're seeing their doctor on a regular basis anyway.

As an example of how the conversion could potentially work, the companies cite AstraZeneca (NYSE: AZN), which was successful getting patients off OTC antacids and onto prescription Prilosec when it launched.

At a market cap of$1.3 billion, investors don't appear to be expecting a very fast launch. With an approval in hand, Ironwood looks like a fairly low-risk stock at this price, with a potential kicker if Linzess can get out of the gates faster than expected. Be sure to follow these companies by adding them to your free personalized watchlist.