A study performed in France tested 54 drugs and found that the metabolism of 42 of the drugs was altered by combining them with grapefruit juice. The reason for this is that grapefruit juice and other citrus contains naringin which is a substance than can affect the medication break down action of enzymes in the gut. The action of these enzymes, known as CYP3A enzymes, are diminished or enhanced by grapefruit juice in many people.
Some of the effects of ‘party’ drugs containing amphetamines are enhanced by combining the drug with grapefruit juice. This reported increased effect has not been well studied but there is reason to believe that the metabolism of amphetamines such as Adderall and Methylphenidate will be different if consumed with a citrus such as grapefruit.
It is possible that when you consume your stimulant medication with grapefruit juice or other citrus, more of the stimulant medication will stay in your blood stream and this will increase substantially the potency of your medication. The danger is that the increase can reach dangerous levels and can, in the worse case, cause life threatening side effects.
As ever present as citrus juice is on our morning breakfast table, few studies have been performed on the interaction of citrus and medicines but most physicians agree that you should avoid drinking grapefruit juice within an hour of consuming any medication.
Over the holidays I spent some time with my aunts and uncles. One of my uncles had a near fatal allergic reaction to his blood pressure medicine. The medicine reached an increased level because he took it while eating grapefruit and he ended up in ICU for 10 days after his tongue and throat swelled (angiodema) closing his wind pipe (trachea). I decided to post about this interaction because I realized that, though it is well known in the medical community, most non-medical people are unaware of citrus/medication interactions.
Unfortunately for him, he has now developed an angioedema reaction to many other drugs and foods as a the result of this interaction of grapefruit and his ace inhibitor drug. About 10% of people treated with Ace Inhibitors will have an angioedema reaction like my uncle had and a few of them will develop idiopathic angioedema (when you start to swell for unknown reasons).
You can still drink your coffee with grapefruit juice as the effects of caffeine and naringin have been studied and the effect and levels of caffeine are not changed by the citrus, Do not, however, take your Inattentive ADHD or Sluggish Cognitive Tempo medications or supplements with grapefruit juice as it is likely that the effects of these therapies will be affected.
Grapefruit juice and drugs: a hazardous combination?
Lohezic-Le Devehat F, Marigny K, Doucet M, Javaudin L.
Therapie. 2002 Sep-Oct;57(5):432-45.