Ironwood Pharmaceuticals and Forest Laboratories are celebrating after getting the green light from US regulators for their bowel drug Linzess.

The US Food and Drug Administration has approved Linzess (linaclotide) to treat chronic idiopathic constipation and irritable bowel syndrome with constipation (IBS-C) in adults. The thumbs-up is based on studies involving almost 2,900 patients which showed that the once-daily capsule was more effective in reducing the amount of abdominal pain and increasing the number of complete spontaneous bowel movements compared with placebo.

Analysts believe that Linzess is going to be a blockbuster principally because of the pain relief it offers. Developed by Ironwood, it is licensed to Almirall in Europe and to Astellas in Asia.

The market is considerable and according to the National Institutes of Health, 63 million Americans are affected by chronic constipation and 15.3 million people suffer from IBS. Supplements and laxatives are usually the first treatments offered and Sucampo/Takeda/Abbott's Amitiza (lubiprostone).

However, Linzess is expected to blow Amitiza out of the water, given that the latter's efficacy is limited and it can cause nausea and abdominal pain. The Ironwood/Forest drug, which should not be used in patients aged 17 and younger, will be launched in the fourth quarter.