That is so interesting that I had to look up some info on it. From what I've read, the reason not to have grapefruit is that there's an enzyme in it that increases the effect of certain medications. Here's a technical explanation, as I am not good at explaining things:
Grapefruit juice is a potent inhibitor of the intestinal cytochrome P-450 3A4 system (specifically: CYP3A4 - mediated drug metabolism) which is responsible for the first-pass metabolism of many medications. This interaction can lead to increases in bioavailability and corresponding increases in serum drug levels. In many cases, the increased serum drug levels can produce some readily observable symptoms. Here are a few examples of adverse effects that are possible when the following medications are taken concurrently with grapefruit. (1) Excessive sedation: benzodiazepines.
I left out the others since you are only concerned with Valium. Added with edit ---- oops, I thought you were concerned with Valium but that was bkfree. Chances are that the medication you were warned about falls into the category of benzowhatevers. You may want to take your meds to your pharmacist and ask.
Wow, I learned something new today. :)
If you love grapefruit so much, I would suggest talking to your doctor about an alternative drug, however, looking at the listing of drugs, I am not sure what would be a good substitute. I take Xanax-XR (extended release) once a day and there is no warning about grapefruit on it. I've also taken Klonopin in the past and it had no warning on it. I'm pretty sure those fall into the category of benzodiwhatevers.
Here's a listing of the drugs that grapefruit affects:
amiodarone astemizole alprazolam atorvastatin
benzodiazepines buspirone carbamazepine carvedilol
cerivastatin cilostazol clarithromycin Clomipramine
codeine cyclosporine dapsone dextromethorphan
diazepam diltiazem estrogens erythromycin
felodipine fentanyl finasteride haloperidol
indinavir lercanidipine lidocaine lovastatin
midazolam methadone nelfinavir nifedipine
nicardipine nimodipine nisoldipine nitrendipine
ondansetron paclitaxel progestins progesterone
quinidine ritonavir salmeterol saquinavir
simvastatin tacrolimus trazodone triazolam
vincristine zaleplon zolpidem
I wish you luck in finding a solution. I personally don't eat grapefruit - doesn't tork my turtle! Now I'd drink grapefruit juice if it had a little vodka in it.... ;)