Why can't you
eat grapefruit
with your pills?
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The full narration of the video.
"No grapefruit with your pills" is only half right. There's a big pomelo on the table, and your parents just took their blood-pressure pills. Can they have a slice? Let's follow one pill on its trip and see where the fruit gets in the way.
You swallow it, it dissolves in the stomach, moves on to the small intestine, and slips through the gut wall into the blood. But the gut wall has guards on duty. They recognise certain drugs, break most of them down on the spot, and let only a small share through.
Doctors already count on that when they set the dose. One pill, and just the right amount reaches the blood. Grapefruit carries a group of substances that knock these guards out. With the guards down, nothing stops the drug, and it all floods into the blood.
For one cholesterol drug, a glass of grapefruit juice a day pushed the amount in the blood to more than three times normal. You take one pill, and your body gets what feels like three. Too much drug brings side effects. Blood-pressure pills can drop the pressure too far and make you dizzy, and some cholesterol pills can hurt the muscles.
Worse, the guards that go down don't get back up. The gut has to grow new ones to take over, which takes a day or two, sometimes three. So juice in the morning and pills at night doesn't help. A few hours apart is not enough.
Those guards are an enzyme in the gut wall whose job is to break drugs down; what knocks it out is a family of chemicals in grapefruit called furanocoumarins. In the drug-interactions section of a medicine leaflet, you'll often find the word grapefruit. In Chinese, it goes by two names, and both mean this same fruit. So why only half right?
The guards only break down drugs they recognise. Plenty of common medicines never pass their checkpoint, so grapefruit changes nothing; and drugs given by injection or drip skip the gut entirely. The ones that can cause trouble are mostly certain blood-pressure drugs, cholesterol drugs, and drugs taken after organ transplants. Now the fruit side. Grapefruit is the best known, and some pomelos, bitter oranges and limes have the same chemicals, while ordinary sweet oranges have almost none.
Pomelos come in many kinds with very different amounts, and nobody can test each one for you. So if you're on medication and want some, check the leaflet first, and when in doubt, ask your doctor or pharmacist. Tonight, go through the medicine boxes at home and look for that word. How many of them mention it?
That rule is
only half right
With grapefruit, some pills put several times more drug into your blood. But not every pill is affected, and not every citrus fruit does it.
There's a big pomelo (a giant Asian cousin of grapefruit) on the table, and your parents just took their blood-pressure pills. Can they have a slice? To answer that, let's follow one pill on its trip.
Guards on
the gut wall
You swallow a pill. It dissolves in the stomach, moves to the small intestine, and passes through the gut wall into the blood. On that wall stand guards. They recognize certain drugs, break them down one by one, and let only a small part through.
Your doctor already counts on this when choosing the dose. One pill, and just the right amount reaches your blood.
Grapefruit
knocks the guards out
Grapefruit contains a group of substances that knock these guards out. With the guards down, nothing stops the drug, and it all rushes into the blood.
For one cholesterol drug, a glass of grapefruit juice a day made the amount in the blood more than three times higher. You take one pill; your body gets what feels like three.
More drug means more side effects. A blood-pressure pill may push pressure too low and make you dizzy. Some cholesterol pills can harm muscles.
Fallen guards
can't get back up
Once knocked out, these guards are broken. The gut has to grow new ones to take over. That takes a day or two, sometimes three.
So juice in the morning and pills at night doesn't help. A few hours apart is not enough.
"Grapefruit"
on the leaflet
The guards' real name: an enzyme in the gut wall that breaks down drugs (CYP3A4). What knocks it out: furanocoumarins in grapefruit.
In the "interactions" section of a medicine leaflet, you will often see the word "grapefruit".
A little extra: a Canadian researcher found this by accident in 1989. He was testing alcohol with a blood-pressure drug and used grapefruit juice to hide the taste of the alcohol. Drug levels in the blood came out surprisingly high.
Not every drug
minds grapefruit
The guards only break down drugs they recognize. Many common drugs never go through this gate, so grapefruit does nothing to them. The trouble is mostly with some drugs in these groups:
Within one group, some drugs are affected and some are not, so it goes drug by drug. If you take pills every day, this is worth knowing (how daily pills differ from a cure: see this one).
Not every citrus
has it
Grapefruit is the famous one. Some pomelos, Seville (bitter) oranges and limes have it too. Ordinary sweet oranges have almost none.
Pomelos come in many varieties, and the amount varies a lot: some tested as strong as grapefruit juice, some much weaker. Nobody can test each one for you.
On pills,
craving citrus
Not sure? Ask a doctor or pharmacist. Even if the leaflet says nothing, you can bring the box and ask. And don't stop or switch your medicine on your own because of grapefruit.
For some drugs, doctors check the level in your blood with a blood test (how blood tests spot problems: see this one).
For those, spacing them
a few hours apart won't help.
Quick check
You drink a big glass of grapefruit juice in the morning and take an affected pill at night. Is that safe?
Grapefruit breaks the gut-wall guards for good; the gut must grow new ones, which takes a day or two, sometimes three.
