Be careful: Grapefruit can change how medicine gets into your body

Q: There's a sticker on my prescription bottle that says not to eat grapefruit or drink grapefruit juice with it. I love grapefruit. Is it okay to have grapefruit juice for breakfast and take my pill in the evening instead?

Your medicine's "grapefruit effect" doesn't wear off that fast. After drinking a glass of grapefruit juice or eating half a grapefruit, it can take up to 3 days for its effect on medicine to wear off completely.

Penny is 87 years old and comes to our clinic every 6 weeks to have her blood thinner level checked. The blood test we do is called an INR. For her, the result should be between 2 and 3. Last month, she started having more bruising than usual. Her blood thinner level also changed, jumping from her previous level of 2.2 all the way up to 4.5. Why had her blood thinner level increased significantly? What was the difference?

Penny lost her husband 2 months ago and now only cooks for herself. Last month, she started eating fresh grapefruit sections several times a week. "It's easy to fix, and I love grapefruit."

I asked Penny to stop eating grapefruit. Once she did that, her blood thinner level dropped back to normal. Grapefruit and grapefruit juice can change the way your body absorbs certain medicines. This "grapefruit effect" was discovered by accident. In 1991, researchers wanted to find out if drinking alcohol while taking a blood pressure medicine called felodipine would change the level of the drug in the blood. They created a study that measured blood pressure and blood levels of the medication twice, once with alcohol in their blood and once without it.

To keep the participants from guessing whether they were taking actual medicine or dummy medicine, the researchers needed a way to disguise the taste of alcohol.

The researchers chose grapefruit juice to disguise the taste of the alcohol. Each participant drank a small glass of grapefruit juice with the medicine. Alcohol was added to the grapefruit juice in half of the doses.

Something curious happened. ALL of the study participants had lower blood pressures than the researchers expected. Not only that, but the blood levels of the medicine were nearly 50% higher than typical. They discovered that drinking alcohol didn't affect the blood level of felodipine, but drinking grapefruit juice did.

What did the grapefruit juice do to cause the blood level of the medicine to rise?

Grapefruit can change how medicine gets into your body. Although most pills dissolve in your stomach, they don't actually get into your bloodstream from there. Vitamins, minerals, nutrients, and medicines are transported into your bloodstream by your small intestine, lined with special cells and molecules working to make this happen.

One particular type of molecule is an enzyme called CYP3A4. Its job is to take apart and change the shape of certain medicines. Once this happens, the drug stops working for you, and your body gets rid of it.

Grapefruit juice and fresh grapefruit contain natural compounds that neutralize the CYP3A4 enzymes lining your small intestine. Without these enzymes available to inactivate part of each dose, you will absorb more medicine.

This "grapefruit effect" is not consistent with everyone or with every medicine. Some medicines are more affected by the CYP3A4 enzyme than others. There are genetic differences in how many CYP3A4 enzymes we have and how active they are.

Eating one grapefruit or drinking 7 ounces of grapefruit juice can completely inactivate your intestinal CYP3A4 enzymes for up to 3 days. Like Penny discovered, if you take a drug that's affected by grapefruit and drink fresh grapefruit juice or eat grapefruit, the level of medicine in your blood can jump by 50%.

Here are 3 Tips for Taking Medication and Grapefruit Safely:

1. Check for the interaction.

Medicines affected by grapefruit usually have a small sticker on the side of the prescription bottle.

2. Avoid fresh grapefruit.

One glass of fresh grapefruit juice can affect your medicine for up to 3 days. Unfortunately, you can’t avoid the interaction by taking them at different times. When taking a medication with a grapefruit interaction, it’s best to avoid grapefruit juice and grapefruit entirely. Grapefruit juice reconstituted from frozen juice doesn't affect medicines like fresh grapefruit or grapefruit juice.

3. It’s safe to eat and drink most citrus fruit.

Although mostly seen only with grapefruit, two ounces of lime juice may increase the level of medication in some people. Oranges, lemons, and other citrus do not affect medicines.

Dr. Louise Achey, Doctor of Pharmacy, is a 44-year veteran of pharmacology and the author of Why Dogs Can’t Eat Chocolate: How Medicines Work and How YOU Can Take Them Safely. Get clear answers to your medication questions at her website and blog, TheMedicationInsider.com. 2023 Louise Achey