According to the FDA, the CYP3A4 enzyme in your small intestine typically breaks down your medication. Grapefruit juice prevents this enzyme from doing its job, so more of your medication gets into your blood at a given time and stays there. Seville oranges, tangelos, and pomelos could also block this enzyme.
The study looked at the effects of both tomato juice and grapefruit juice on how two drugs are processed in the body. Nifedipine is a calcium-channel blocker that treats high blood pressure, and midazolam is a sedative that slows down the nervous system. Both drugs are metabolized by the CYP3A4 enzyme. When rats were given grapefruit juice before taking the drugs, it significantly increased their concentration levels in the blood. Tomato juice also had the same effect on the midazolam but no effect on the nifedipine. The study suggests that, like grapefruit juice, tomato juice can influence how the body handles certain drugs, but the extent of the effect may vary depending on the specific drug.