11, 12 Seville oranges, (often used in marmalades), limes and pomelos also produce this interaction.

However, there are no case studies in which consuming grapefruit juice while taking metformin led to adverse effects in humans. The study was undertaken to evaluate the effect of quercetin on the pharmacokinetics of Metoprolol tartrate. A single dose in vivo pharmacokinetic study was carried out in rat models. However, there is little evidence to suggest people taking metformin should avoid grapefruit. A few medications should be avoided when eating grapefruit. We need you to answer this question! The Wikipedia article at Grapefruit–drug interactions - Wikipedia contains a list of interactions of grapefruit with various medications. Grapefruit juice increases the level of simvastatin in your blood and makes side effects more likely.

One whole grapefruit or 200 mL of grapefruit juice is sufficient to cause clinically relevant increased systemic drug concentration and subsequent adverse effects. Grapefruit does lead to negative interactions with some medications. In this study, rats were treated with quercetin (10 mg/kg) and metoprolol tartrate (20 mg/kg) orally and blood samples were collected 0, 0.25, 0.5, 0.75, 1, 1.5, 2, 4, 8, 12 h post treatment. Does grapefruit interfere with metoprolol? Fexofenadine's absorption can be decreased when taking antacid medications and drinking fruit juices, such as apple, orange or grapefruit juice, according to Drugs.com2'). However the article itself states that the list is incomplete.
Atorvastatin interacts with grapefruit juice if you drink large quantities (more than 1.2 litres daily), but an occasional glass is thought to be safe. Consuming grapefruit or grapefruit juice can affect the safety and effectiveness of a variety of drugs. Grapefruit juice or grapefruits themselves can be healthy snacks. There are no β blockers on the list.