Pharmaceutical company Indivior (LON:INDV) warned that the release of a generic version of one of its best-selling drugs will likely have a “materially higher” impact on profits than first anticipated.

First-half net profit fell by 6 percent to $162 million from $153 million year earlier, and net revenue fell by 5 percent to $524 million from $553 million.

The company blamed the fall in revenue on tactical rebating and unfavourable mix due to increased growth in its most price sensitive channel, Medicaid. This more than offset both strong US market growth, largely driven by the Medicaid channel, and rest of world growth.

The company had previously warned on the potential impact of the release of a generic version of its Suboxone Film, saying that it was likely to hit profits by about $25 million. They have now said it may well be “materially higher”.

“Our primary focus is to ensure the successful progression of Sublocade as it begins its transformation of the treatment of opioid use disorder,” said Shaun Thaxter, CEO of Indivior.

Shares in Indivior are currently down 20.33 percent at 265.70 (0914GMT).