Grapefruit Juice - Is It Always Healthy?
Doctor of Pharmacy Candidate, 2001
Ohio Northern University
you have a glass of grapefruit juice with breakfast this morning?
Have you taken your morning medications? Do you know if grapefruit
juice can interact with your medications?
Mr. X did not know. This
healthy 29-year-old male woke up one morning and took his common
allergy medicine, terfenadine. He had been taking this medicine
twice a day for more than a year. He also liked drinking grapefruit
juice 2 or 3 times a week and sometimes more often. On this
day, he drank two glasses of grapefruit juice and went out to
mow the lawn. Moments later, he collapsed and died due to a
fatal heart problem.
Even though he had taken
exactly the amount prescribed for him, the coroner found that
the allergy medicine had reached a dangerous level in his blood.
It appeared that grapefruit juice slowed down the body's ability
to break down this drug. This may have led to the toxic amounts
of the medicine that killed Mr. X.
The Food and Drug Administration
(FDA) did not know about these side effects when the medicine
was approved. The FDA removed this medicine from the market
in 1997 because of the possibility of serious side effects on
While this problem has not
been seen with other allergy medications, terfenadine is not
the only medication affected by grapefruit juice! If we only
knew then what we know now, Mr. X might still be alive. Every
person who is taking medications should check to see if it is
safe to drink grapefruit juice.
"Why does grapefruit
juice interact with some medications and not others?"
It is not known exactly
what grapefruit juice contains that causes these drug interactions.
Some researchers think that narningenin, DHB, or both are the
compounds in grapefruit juice that may be responsible for the
What we do know is that some drugs need certain natural enzymes
in the body to break them down so that medicine can be eliminated
from the body.
Grapefruit juice interferes
with one of these enzymes, CYP3A4. It may cause some medicine
to build up in the body, leading to unwanted side effects. The
amount of CYP3A4 found in a person will vary from person to
person. People with higher amounts of the enzyme are affected
when grapefruit juice is taken with medicine more often than
people with lower amounts.
"Do other types of juices
or eating a grapefruit interact with medications?"
Not all citrus juices contain
narningenin or DHB. For this reason, citrus juices such as orange
juice have not been shown to affect this enzyme.2
Different parts of the grapefruit
also contain different amounts of these two substances. The
peel of the grapefruit is thought to contain more than any other
part of the fruit. It is uncertain if eating a grapefruit will
cause the same effects as drinking grapefruit juice.
Even different brands of
grapefruit juice may have different amounts of these two substances.2, 3
The way the grapefruit juice is processed may be one of the
reasons for this. When companies make grapefruit juice, machines
use enough pressure to squeeze these substances from all parts
of the grapefruit. The consumer does not know how much of these
compounds are in the different products. It would be helpful
for consumers if the labels of grapefruit juice products contained
a warning statement such as "This product contains substances
that may interact with certain prescription drugs."
A common misconception
is that it takes large amounts of grapefruit juice to interact
with medications.1 An 8 oz glass of regular
strength grapefruit juice has a similar effect as two or three
glasses of double-strength grapefruit juice.
"Do my medications interact
with grapefruit juice?"
Every time you are prescribed
a new medicine check with your doctor or pharmacist about possible
grapefruit juice interactions.
If you have not been drinking
grapefruit juice, then do not add it to your diet until you
know if it is safe for you. If you are already taking any of
your medications with grapefruit juice, do not stop taking it
without talking to your doctor first. When you stop drinking
grapefruit juice, your doctor may need to adjust the dose of
The following is a partial
list of medication that interacts with grapefruit juice in some
cyclosporine (Sandimmune)1, 2, 3
erythromycin (E-Mycin, Ery-Tab, E-base, E.E.S., Ery-Ped)
felodipine (Plendil)1, 2, 3, 4
methadone (Dolophine, Methadose )2
midazolam (Versed)1, 2, 4, 5
nifedipine (Adalat, Procardia )2, 3
nimodipine (Nimotop)2, 3
nisoldipine (Sular)1, 2, 3, 5
saquinavir (Fortovase, Invirase )3
Not all of these medications
in combination with grapefruit juice will produce as severe
a reaction as the one described in the beginning of the article.
Researchers continue to investigate grapefruit juice interactions
to better predict which medicine should not be taken in combination
with grapefruit juice.
Until all the facts are
known, ask your pharmacist if your medicine interacts with the
antibiotic erythromycin. If it does, then there is a high chance
that the medicine will interact with grapefruit juice too.
Before you take your next
pill, remember that grapefruit juice has the potential to interact
with many prescription drugs. Grapefruit juice may not be healthy
1. Spence J.D. Drug interactions with grapefruit
juice: Whose responsibility is it to warn the public? Clin
Pharmacol Ther 1997;61: 395-200.
GC, Lipsky JJ. Drug-grapefruit Juice Interactions. Mayo Clin
Drug Interactions with Grapefruit Juice. Drug Safety 1998 Apr;
18 (4): 251-272
.© 2001 Consumer Health
Information Corporation. All rights reserved.