Oprah Winfrey said she’s stepping down from her role at WeightWatchers after serving on its board of directors for nine years. She also pledged to donate her financial stake in the weight-loss company to the National Museum of African American History and Culture.

Winfrey’s announcement, issued late Wednesday, sent shares of WeightWatchers into a tailspin. In premarket trading, shares plunged 25%. 

Winfrey joining WeightWatchers in 2015 gave the weight-loss company a high-profile boost, with its shares more than doubling soon after the deal was announced. But in recent years, WeightWatchers and other diet companies have struggled amid a shift toward so-called GLP-1 drugs like Ozempic, which rely on hormones to control appetite and have helped people shed extra pounds. 

The media star’s decision comes after she disclosed last year that she relies on these drugs to maintain her weight. Winfrey told People magazine in December that she “released my own shame about it” and went to a doctor to get a prescription, although she didn’t disclose the name of the medication she relies on. Winfrey added, “I now use it as I feel I need it, as a tool to manage not yo-yoing.”

WeightWatchers, officially named WW International, last year moved into the prescription weight-loss drug business by purchasing Sequence, a telehealth provider that offers users access to GLP-1 drugs. It also debuted WeightWatchers GLP-1, a subscription program for people using that class of drugs. 

In her statement, Winfrey said she will continue “to advise and collaborate with WeightWatchers and CEO Sima Sistani in elevating the conversation around recognizing obesity as a chronic condition, working to reduce stigma and advocating for health equity.”

Winfrey said she’s donating her shares in WeightWatchers to the National Museum of African American History and Culture, a Smithsonian institution in Washington, D.C., as she’s been a long-time supporter of the organization. 

In the statement, WeightWatchers said Winfrey’s decision to donate her shares is partly “to eliminate any perceived conflict of interest around her taking weight loss medications.”