AstraZeneca shareholders have voiced concerns regarding potential mega-merger talks with US rival Bristol Myers Squibb (BMS). Investors question the value of acquiring a company facing significant revenue loss due to patent expirations, especially as AstraZeneca has its own robust pipeline and revenue targets. Shares in AstraZeneca fell approximately 9 per cent following reports of the potential deal, which could create a drugmaker valued near $400bn.

Key criticisms include BMS's looming patent cliff, which could lead to the loss of nearly half its revenues. Rathbones, a top AstraZeneca shareholder, noted the surprise of the talks given AstraZeneca's organic growth trajectory and its target of increasing annual revenues to $80bn by 2030. Concerns were also raised about potential antitrust issues and the strategic sense of such a large merger, with past mega-mergers often cited as value destroyers.

Despite these reservations, some investors see potential benefits, including complementary oncology pipelines, significant cost savings, and increased US market exposure. The deal's approval would likely require shareholder consent from both companies. Neither AstraZeneca nor BMS has officially commented on the ongoing discussions, and the outcome remains uncertain.