CBD and grapefruit: drugs interactions

Research shows that CBD is safe, therapeutic, and has few side effects.  However, there is one important caveat to using cannabidiol: CBD interacts with some common medications by affecting how the body metabolizes these substances (including antihistamines, benzodiazepines, certain antidepressants, and statins).  And while scientists continue to study the specifics of CBD action, the general recommendation is not to use CBD with medications that have grapefruit warnings.

What does the "grapefruit warning" on the medicine mean?

Grapefruit or its juice should not be taken with certain types of medicine (see below).  The reason is that grapefruit contains substances that increase the bioavailability of many drugs [1].

Why is it undesirable to increase the bioavailability of the medicinal product?

An increase in the bioavailability of the drug leads to an increase in its concentration in the blood, which, firstly, might increase the side effects. Second, increased bioavailability disrupts the dose calculation.  After all, a low dose can become high due to improved absorption of the drug in the intestines, or the drug will not be excreted from the body in time due to inhibition of liver enzymes.  Therefore, the risk of overdose increases.  In addition, some drugs have a narrow "therapeutic window", meaning concentration of the drug in the blood must be within a certain range, while higher concentration loses beneficial effect [2].

Why is CBD compared to grapefruit?

Cannabidiol inhibits function of the same intestinal enzymes as does grapefruit [3].  Moreover, in addition to the intestines, CBD also inhibits liver enzymes, so CBD effect on the bioavailability of the drugs is rather greater than that of grapefruit juice [4].

How long does CBD/grapefruit effect on the drugs pharmacokinetics last?

If you drink a glass of grapefruit juice in the morning, the bioavailability of drugs can increase for up to three days [5]. The reason is that restoring enzyme activity to its baseline is a slow process. Since CBD inhibits more enzymes than grapefruit, the effects of cannabidiol may be even longer-lasting [3].

What medications should not be taken with CBD or grapefruit?

Of course, you should check with your doctor if you are on medication and considering starting CBD. In general, the enzymes that are affected by grapefruit or CBD break down most prescription and over-the-counter drugs.  Among the drugs that are recommended against combining with grapefruit juice or CBD are the following types of meds:

●     cholesterol-lowering statins such as Zocor (simvastatin) and Lipitor (atorvastatin);

●     medicines to treat high blood pressure, such as Procardia and Adalat CC (both nifedipine);

●     medicines to prevent rejection of transplanted organs, such as Neoral and Sandimmune capsules or oral solution (both cyclosporine);

●     anti-anxiety medications such as BuSpar (buspirone);

●     corticosteroids, particularly for Crohn's disease, such as Entocort EC and Uceris tablets (both budesonide);

●     drugs to normalize heart rhythm, such as Pacerone and Cordarone (both amiodarone);

●     antihistamines such as Allegra (fexofenadine) [6].

References:

1. https://www.healthline.com/health/cbd-and-drug-interactions-what-you-ne....

2. https://www.nhs.uk/common-health-questions/medicines/does-grapefruit....

3. https://www.forbes.com/sites/davi...

4. https://www.health.harvard.edu/blog/cbd-and-other-medications-proceed-with-cau....

5. https://www.health.harvard.edu/staying-healthy/grapefruit-and-medication-a-cau....

6. https://www.fda.gov/consumers/consumer-updates/grapefruit-juice-and-some-dr....