Abnormal returns in stock markets are subject to many studies. In particular, the ability to test on specific industries has received much attention. The number of M&As have increased in the last decade, which also includes M&A deals in the pharmaceutical (pharma) industry, where companies acquire to reach distinctive capabilities to survive in the dynamic and complex business environment. Companies also utilize M&A to increase their ability to create shareholder wealth, though this has shown partially not to be correct. Previous studies conducted, have found rather different results on M&A transactions. This thesis examines the impact on shareholder wealth in pharmaceutical M&As, more precise the study tests the abnormal stock return around the announcement day. The study is conducted with a data sample consisting of 250 deals in the pharma industry between 2000 and 2014.