We know you sometimes have burning questions that can best be answered by a pharmacist. Our feature, Ask Your Pharmacist , seeks to address some of those issues. Get answers by sending your questions to healthandwealth@jamaicaobserver.com.

Question: Why can’t I eat grapefruit with some medications?

Answer: Citrus fruits — oranges, grapefruits, limes, and tangerines — are great to have in our diets. However, grapefruit, in particular, can have negative effects on some of the medications that we take.

In some cases, grapefruit increases the amount of drug entering the bloodstream.

Some cholesterol medications (for example, simvastatin, atorvastatin/Lipitor) and some blood pressure medications (for example, nifedipine, felodipine/Plendil) are affected by grapefruit juice. The grapefruit juice lets more of the drug enter the bloodstream, leading to more side effects. Many drugs are broken down by an enzyme in the small intestine called CYP3A4. Grapefruit juice blocks the action of this enzyme, so the drug is not broken down and more enters the bloodstream.

On the other hand, grapefruit juice can have the opposite effect on some drugs.

Grapefruit juice causes less Allegra (Fexofenadine) to enter the bloodstream, decreasing how well the drug works. In fact, other fruit juices like orange juice and apple juice also decrease the effectiveness of Allegra. In this case, grapefruit affects proteins in our bodies called drug transporters. If the drug transporters are no longer able to move drugs into our cells, then less of the drug will be absorbed.

The effects of grapefruit juice can last for more than 24 hours. Hence, taking the medication at a different time from the grapefruit juice will not prevent the interaction.

Men, please note that Viagra and Cialis — used to treat erectile dysfunction — are also affected by grapefruit juice! Grapefruit juice inhibits the body’s absorption of these drugs. Hence, grapefruit juice makes these medications less effective.

Men, if you want a good erection, please do not eat or drink any grapefruit products while taking Viagra or Cialis.

If you are on long-term medication that interacts with grapefruit, you might have to consider removing grapefruit from your diet. Pay attention to soft drinks and other juices, which may contain some amount of grapefruit juice. You can eat other citrus foods from which you can get a ton of antioxidants.

Be sure to ask your pharmacist if grapefruit juice interacts with your medication.

Novia Jerry Stewart, MSc, RPh, is a pharmacist who specialises in ophthalmic care. She earned a Bachelor of Pharmacy degree at the University of Technology, Jamaica and a Master of Science in General Management at Walden University in Minnesota, USA. She also has a Certificate in Diabetic Retinopathy Grading from the University of Melbourne, Australia, and a Diploma in Opticianry from the University of Central Florida. She may be contacted at novia_jerry@yahoo.com.