The healthcare index was down 0.25% at 0853 GMT, while the pan-European benchmark STOXX 600 added 0.15%.
Trump aims to lower drug prices in the U.S. by linking them to those of other nations and expanding the scope of a July action.
Analysts estimate that more than 60% of global pharmaceutical profits are generated in the United States due to the high drug prices.
Credit Suisse analysts said that the impact of the executive order would be negative if implemented and that some was resistance from the industry.
European shares that could be hit by the U.S. move include AstraZeneca, GlaxoSmithKline plc, Novartis, Roche, Sanofi, Bayer and Novo Nordisk A/S, according to Credit Suisse.
By Joice Alves