Big mergers aren’t always all they’re cracked up to be. Regulatory pressures can keep deals from ever getting off the ground, with the largest tie-ups attracting special scrutiny. Even when they are consummated, the failure rate can top 60% based on share price, according to some studies.

Recent disappointments include the 2015 merger of Kraft/Heinz/3G Capital, whose shares have lost half their value; Verizon’s 2017 acquisition of Yahoo and its earlier buy of AOL, which resulted in a huge write-down last year; and Bayer’s 2016 acquisition of Round-Up-maker Monsanto, which is fighting multimillion dollar verdicts in the U.S. over alleged links to cancer in users. Other deals fell through entirely, such as Rite Aid’s proposed $24 billion merger with Albertsons last year.