Shire Pharmaceuticals ( SHPGY) fell 26% in Instinet premarket trading after warning that competitive pressure may dampen growth in 2002.

The British specialty drugmaker faces stiff competition from generic versions of Adderall, Shire's top-selling hyperactivity drug. Additionally, new marketing expenses are expected to impact the company's results.

Shares of Shire were recently trading at $24 after closing yesterday at $32.45.