Ackman's 2012 short against multilevel marketing supplement maker Herbalife was one of the most high-profile missteps of his career, according to Investopedia. Ackman bet $1 billion that the company would fail, while fellow billionaire investor Carl Icahn made a long-term investment in the company, Business Insider previously reported. Ackman publicly accused Herbalife of being a pyramid scheme whose stock price was bound to hit zero, according to The Wall Street Journal.
Icahn and Ackman got into a public fight over the company's prospects that was called "the hedge fund equivalent of Stalingrad" by The Journal, with Icahn eventually emerging victorious. Ackman lost hundreds of millions of dollars on Herbalife, Business Insider reported.
Ackman also made a controversial investment in near-bankrupt drugmaker Valeant Pharmaceuticals that resulted in a contentious Senate hearing over Valeant's practice of buying existing drugs and selling them at inflated prices in 2016, Business Insider reported at the time. Valeant has since been renamed Bausch Health.
Pershing Square also lost money on bets on now-defunct bookseller Border's Group and big-box retailer Target Corporation, according to Investopedia. The losses put the hedge fund into what Bloomberg called a "three-year losing streak" in 2019, before Ackman's bet against the stock market.