GSK and Actelion discontinue clinical development of almorexant

Issued: London UK

GlaxoSmithKline (GSK) and Actelion Ltd (SIX: ATLN) today announced that clinical development of the Phase III investigational dual orexin receptor antagonist, almorexant, has been discontinued. This decision follows a review of data from additional clinical studies, which were conducted to further establish the clinical profile of almorexant, including the tolerability profile.

GSK and Actelion remain committed to conducting further research to better understand the potential of orexin receptor antagonism in sleep disorders and other indications. Both companies will continue to work on the discovery and development of new orexin receptor antagonist therapies, based on the orexin alliance formed in July 2008.

GlaxoSmithKline – one of the world’s leading research-based pharmaceutical and healthcare companies – is committed to improving the quality of human life by enabling people to do more, feel better and live longer. For further information please visit www.gsk.com.

Actelion Ltd – a biopharmaceutical company with its corporate headquarters in Allschwil/Basel, Switzerland. Actelion's first drug Tracleer®, an orally available dual endothelin receptor antagonist, has been approved as a therapy for pulmonary arterial hypertension. Actelion markets Tracleer® through its own subsidiaries in key markets worldwide, including the United States (based in South San Francisco), the European Union, Japan, Canada, Australia and Switzerland. Actelion, founded in late 1997, is a leading player in innovative science related to the endothelium - the single layer of cells separating every blood vessel from the blood stream. Actelion's over 2,400 employees focus on the discovery, development and marketing of innovative drugs for significant unmet medical needs. Actelion shares are traded on the SIX Swiss Exchange (ticker symbol: ATLN) as part of the Swiss blue-chip index SMI (Swiss Market Index SMI®). www.actelion.com

GlaxoSmithKline cautionary statement regarding forward-looking statements Under the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995, GSK cautions investors that any forward-looking statements or projections made by GSK, including those made in this announcement, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Factors that may affect GSK' s operations are described under 'Risk Factors' in the 'Business Review' in the company' s Annual Report on Form 20-F for 2009.