Viagra made by Pfizer and Nexium made by AstraZeneca.

Pfizer's attempt to gain control of U.K. pharmaceutical company AstraZeneca through a £69.4 billion ($110 billion) bid in May would have run aground on changes to U.S. tax inversion laws, the chief executive of AstraZeneca has told CNBC.

"We were worried about the tax inversion risk – in fact it has become a reality. If we had agreed to a deal at the time, probably that deal would have fallen apart by now, just like the AbbVie/Shire deal, and created enormous destruction and disruption in our company," Soriot told CNBC in an exclusive interview.