"Novo Nordisk also faces a number of potential obstacles that could still hamper its expected growth. The surge of popularity in the drugs — fuelled in part by slimming celebrities — has caused a supply shortage and created a booming black market. Concerns rumble about side effects. Rival Eli Lilly has won approval for its own obesity drug, which could be more effective and currently has a lower list price."

https://www.ft.com/content/d4d289a7-e1a5-4848-8e7e-b592f7018722