Analysts have cut their earnings forecasts for GlaxoSmithKline after the European Medicines Agency banned the sale of its once best-selling diabetes drug Avandia.
US authorities have also placed severe restrictions on its sale after it was linked to a higher risk of heart attacks.
Industry experts said GlaxoSmithKline’s profits are likely to show no growth next year.
Glaxo’s shares fell on both Thursday and Friday.
The move could open the way for newer diabetes treatments to gain market share, such as Merck & Co’s drug Januvia and AstraZeneca and Bristol-Myers Squibb’s Onglyza.