You won’t hear about it (anywhere else but here), but I’m starting to uncover research that shows some things can lower Viagra levels. In this article from the European Journal of Clinical Pharmacology (at this PubMed link: www.ncbi.nlm.nih.gov/pubmed/19830413), it was reported that adults drinking pummelo juice (similar to grapefruit juice) had a 60% drop in Viagra availability. That’s a pretty significant drop!

I’ll research to see if there are other things, and also find out what pummelo juice is. I think it’s something they drink in the Middle East, because the study was done in Jordan.
Article citation and abstract:

Eur J Clin Pharmacol. 2010 Feb;66(2):159-63. doi: 10.1007/s00228-009-0738-0. Epub 2009 Oct 15.

The effects of pummelo juice on pharmacokinetics of sildenafil in healthy adult male Jordanian volunteers.

Al-Ghazawi MATutunji MSAbuRuz SM.

Abstract

PURPOSE:

The main purpose of this work was to investigate the effect of pummelo juice on the pharmacokinetics of sildenafil after oral administration.

METHODS:

This was a comparative, randomized, two-period, two-treatment, two-sequence, single dose, crossover study investigating the effect of pummelo juice on the pharmacokinetics of sildenafil citrate tablets (equivalent to 50 mg sildenafil) in healthy male participants under fasting conditions compared with water as a control. Six healthy normal adult males were administered 50 mg sildenafil with pummelo juice or water at two different periods in a crossover study.

RESULTS:

Study results showed that pummelo juice reduced the rate and extent of sildenafil bioavailability to around 60% [maximum plasma concentration (C(max)); from 212.44 ng/ml to 134.07 ng/ml, 90% confidence interval (90% CI) 44.70-89.11, and area under the plasma concentration time curve from zero to infinity (AUC(infinity)); from 564.51 ng.hr/ml to 336.87 ng.hr/ml, 90% CI 39.17-90.92]. This interaction was opposite to that expected and is speculated to be due to either an effect on transporters or a physicochemical interaction between sildenafil and some components of the juice.

CONCLUSION:

Patients should be advised not to drink pummelo juice before or immediately after taking sildenafil.