Oprah Winfrey says she had one big main side effect from taking a GLP-1 weight-loss drug.

The most common problems for patients taking blockbuster anti-obesity medications like Wegovy and Zepbound are gastrointestinal issues including nausea, diarrhea and constipation.

“I never had nausea or diarrhea, but I did have the third one,” Winfrey told TODAY’s Jenna Bush Hager and Sheinelle Jones during a live interview on Tuesday, Jan. 13.

“I finally figured out, for me, what the right combination of magnesium and water is. I have to drink a lot of water… I have to have a gallon of water a day.”

Winfrey added that she has to drink all of that water before 4 p.m.; otherwise, she’s up all night.

Water helps soften stool and move food through the intestines, easing constipation.

Magnesium citrate helps by causing stool to retain water, softening it, making it easier to pass and increasing the frequency of bowel movements, according to the National Library of Medicine.

Winfrey writes about finally finding weight-loss success with a GLP-1 drug in her new book, “Enough: Your Health, Your Weight, and What It’s Like to Be Free.”

“Oprah’s kidneys are very, very happy,” said Dr. Ania Jastreboff, her co-author and an endocrinologist and associate professor at the Yale School of Medicine.

Every medicine for any disease has side effects, and there’s always a risk-to-benefit ratio to consider, Jastreboff added.

Hydration is also one of the best ways to lessen nausea, a side effect that can frustrate GLP-1 users, as is increasing the dose of the medication very slowly, she said.

“So start low, go slow. If you’re feeling nauseated, then don’t increase the dose,” Jastreboff advised.

“And there’s other things: Not eating past the point of fullness, making sure you’re monitoring which foods could make you (feel) worse. All of these different things can lower the side effects.”