It’s pretty much just an interaction with “nitrates” which are typically taken by people with pretty serious cardiac issues, and usually educated re: the side effects if taken with viagra or similar compounds (cuz you never know if someone has Viagra in their drawer from another pharmacy or years ago or “natural” Viagra from another source).

The interaction with other blood pressure meds appears additive rather than synergistic and Viagra alone only minimally reduced blood pressure. The cough and cold aisle or a cafe presents more dangers.

https://pubmed.ncbi.nlm.nih.gov/10078539/

At least over the counter Viagra would be properly labelled about these things.