What Really Happens If You Eat Grapefruit With Your Medication?

Sure, starting off your day with a halved grapefruit or a glass of its tart juice can be a healthy choice—lots of vitamin C and potassium—but if you take certain drugs, it might actually be just the opposite.

“Grapefruit can affect the functioning of many different medications,” Emily Van Eck, MS, RDN, an Austin-based dietitian nutritionist, tells SELF. Specifically, it can alter the amount that reaches your system, exacerbating or mitigating the intended effects, Van Eck says. So yes, if you’ve ever been told to avoid grapefruit while taking certain meds, know that this advice is legit.

But does it apply to all meds, or are only some drugs at risk? And what about grapefruit juice versus chunks of the actual fruit? Below, we break down everything you need to know about grapefruit and medication interactions so you can stay safe.

How does grapefruit interact with medication in the first place?

In most cases, grapefruit interferes with meds by messing with an enzyme in your intestines called CYP3A4, which plays a role in metabolizing certain drugs. Under normal circumstances, CYP3A4 reduces their absorption and makes it harder for them to enter your bloodstream, but when you eat or drink grapefruit, compounds known as furanocoumarins bind to the enzyme, keeping it from doing its job. The result? The amount of the med that is absorbed and then released into your bloodstream “actually increases,” Yi Guo, PharmD, an associate professor at the Albert Einstein College of Medicine, tells SELF.

And nope, this is not a good thing. Higher levels of the drug can come with an increased risk of side effects. Depending on the med, this can include serious health hazards like liver and muscle damage or even kidney failure.

But in a few cases, as more recent research has shown, grapefruit can actually have the opposite effect on some meds—causing a decrease in the drug concentration within your body. The compounds in grapefruit can hamper the function of proteins known as drug transporters, which ferry the medication into your cells to be absorbed. Ultimately, this allows less of the drug to enter your blood, reducing its effectiveness.

You can expect the effects from grapefruit to stick around for a while—typically around 24 to 72 hours, according to Dr. Guo. Keep in mind that the duration will be proportional to the amount of the fruit too: The more you take in, the longer the effects will last. What’s more, not everyone will react the same way: The effects of grapefruit on meds depend in part on your unique physiology, since the amount of the CYP3A4 enzyme varies from person to person.

Which medications should not be taken with grapefruit?

There are a whole bunch: In a 2013 review published in The Canadian Medical Association Journal, researchers estimated that more than 85 drugs are known or predicted to be affected by grapefruit consumption. Here are a few examples of specific types and products that have been documented to interact with the fruit, according to the FDA. Note that not all drugs in these classes will have the same interactions.