Shire shares slide on copycat drug blow

The maker of a leading hyperactivity drug has suffered a £1 billion hit to its value after a rival was given permission to make a copycat version.

Regulators in the United States approved a cut-price version of hyperactivity drug Adderall XR, which accounted for more than 10% of Shire's product sales in the last quarter, leading analysts to warn of "potentially severe" downgrades to earnings forecasts.