The multi-billion dollar weight-loss drug market has ballooned in the past few years. And the two pharmaceutical companies currently duking it out for market dominance, Novo Nordisk and Eli Lilly, have a century-long rivalry.

Bloomberg News health reporter Madison Muller breaks down how Eli Lilly developed Zepbound, a new drug that can help patients cut more than 20% of their body weight — and why some investors and analysts think it will turn Eli Lilly into the first ever trillion-dollar drug company.

(Corrects characterization of the current size of the weight-loss drug market)