Eating grapefruit can lead to higher doses of a drug in the bloodstream. This recent article from the New York Times describes one mechanism:
"Under normal circumstances, the drugs are metabolized in the gastrointestinal tract, and relatively little is absorbed, because an enzyme in the gut called CYP3A4 deactivates them. But grapefruit contains natural chemicals called furanocoumarins, that inhibit the enzyme, and without it the gut absorbs much more of a drug and blood levels rise dramatically."Those higher doses can be deadly. The article describes...
"The 42-year-old was barely responding when her husband brought her to the emergency room. Her heart rate was slowing, and her blood pressure was falling. Doctors had to insert a breathing tube, and then a pacemaker, to revive her.Lots of drugs interact with grapefruit - benzodiazepines (Valium, Xanax), antidepressants (Zoloft), statins (Lipitor, Zocor), erectile dysfunction drugs (Viagra), antihistamines (Allegra), painkillers (oxycodone, hydrocodone, Tylenol). Wikipedia has a lengthier list.
They were mystified: The patient’s husband said she suffered from migraines and was taking a blood pressure drug called verapamil to help prevent the headaches. But blood tests showed she had an alarming amount of the drug in her system, five times the safe level.
“The culprit was grapefruit juice,” said Dr. Unni Pillai."
This is something I learned years ago in one of my nutrition classes, but my peers and I weren't taking many drugs so it sat on my mental periphery. Not anymore.