As the markets face tariff-related volatility, some companies — especially biotechnology and pharmaceuticals companies — are setting up or extending shareholder rights plans, also known as poison pills, to discourage unsolicited bidders and activist investors seeking to accumulate shares at discounted prices.

“We may see more companies putting pills on the shelf and more pills in general,” proxy solicitor and adviser Tom Ball said. “If you’re a smart company, you’ll have one on the shelf and just pull the trigger and put it in place when you need it.”

Bausch Health Cos. (BHC), which saw its share price drop 43% over the past six months, on April 14 installed a pill that would be triggered if an investor owned 20% or more in shares. The measure was set up to “ensure” shareholders are treated fairly “in connection with any unsolicited takeover bid or other acquisition.” The pill emerged after Alex Meruelo, a Cuban-American billionaire, shifted from a passive 13G to an active 13D and said in an April 7 filing that he may seek to talk to the company on strategic matters and could identify or nominate “strategic individuals” to the board.

In addition, the company said in an Tuesday filing that Carl Icahn, who reached an agreement with the drug company in 2021, had told it that he had economic exposure to 90.7 million shares, in addition to a 9.5%, or 34.7 million-share, stake — making him cumulatively owner of about 35% of the company. Icahn’s son, Brett M. Icahn, joined the drug company’s board in 2021 as part of an agreement.

And biopharmaceutical company Keros Therapeutics Inc. (KROS) on April 10 adopted a limited-duration shareholder rights plan after an undisclosed investor rapidly accumulated its stock and held 11.2% as of April 6. The pill would activate if an active investor owned 10% of shares, or a passive investor accumulated 15% or more. The biopharmaceuticals company also initiated a review of strategic alternatives.

On April 3, Perion Network Ltd. (PERI), a Nasdaq-listed Israeli technology company, said it’s adopted a pill with an unusual 13% trigger — though it didn’t provide any indication that a specific potential buyer had been accumulating.

In other situations, poison pills were extended or adjusted in recent days. In November, Daktronics Inc. (DAKT) responded to a decision by Alta Fox Capital Management LLC to convert promissory notes into shares by extending its poison pill to Nov. 19, 2025. The rights plan was to be triggered if an active investor, such as Alta Fox, owned 15% or more, or a passive investor accumulated greater than 20%. On March 3, however, the dissident investor and digital billboard company reached a settlement, and the pill was terminated.

Meanwhile, on March 26, Lee Enterprises Inc. (LEE) said its board extended an anti-takeover pill after the Hoffmann Family of Cos. submitted an unsolicited expression of interest. Hoffmann, which accumulated a 9.8% stake, on March 20 sent a letter to the newspaper owner seeking to open talks about buying the company, Lee reported March 31. The pill has a 15% trigger.

In March, Pliant Therapeutics Inc. (PLRX), a biopharma company focused on fibrotic diseases, set up a pill with 10% and 20% active-passive thresholds “in response to recent accumulations” of the company’s stock.

Biopharmaceutical company Acelyrin Inc. (SLRN) also in March said its board determined that an unsolicited takeover offer from San Diego-based Concentra Biosciences LLC, an acquisitive portfolio company of Tang Capital Partners LP, didn’t offer superior value to a planned merger with Alumis Inc. (ALMS). On March 13, Acelyrin adopted a pill with 10% and 20% thresholds.

Tang Capital, a life sciences-focused investment company, owns 8.8% and 9% of Acelyrin and Pliant, respectively. Concentra on April 2 agreed to buy Allakos Inc. (ALLK), a biotechnology company focused on developing antibody treatments for allergic, inflammatory and proliferative diseases. Deep Track Capital LP, a sometimes activist, owns a 9.8% Pliant Therapeutics stake.

And in restaurant unsolicited bids, on April 7, El Pollo Loco Holdings Inc. (LOCO), which saw its shares drop 30% over the past six months, disclosed that it entered into a confidentiality agreement with 15% owner and unsolicited bidder Biglari Capital Corp. The Sardar Biglari-led investor submitted an indication of interest on April 6 to buy the fire-grilled chicken restaurant chain. El Pollo Loco adopted a pill with a 12.5% threshold in 2023 after Biglari began accumulating a large stake, and in 2024 it extended the pill and hiked its threshold to 15%.

—Jean Haggerty contributed to this report

Editor’s note: The original version of this article on poison pills was published April 22, 2025, on The Deal’s premium subscription website. For access, log in to TheDeal.com or use the form below to request a free trial.