Indeed. There is the theoretical potential for the two to interact badly, but my understanding is that there simply isn't enough evidence to show the combination is safe for most people, so it is not therefore licenced in the UK.
The bigger issue I would suggest is Dapoxetine side effects in its own right, especially at 60 mg. It is something which should only be considered if you have a true diagnosis of PE. (and is licenced accordingly) It is not for recreational use unlike ED meds which are frequently used that way.
The reality as you know is that many drugs generally have a wide 'abuse' margin for the relatively fit and healthy and for occasional use ... until sometimes they don't 
Good post. I’ll add that I personally think dapoxetine is a nasty looking drug that I didn’t like the look of even when I was ‘young and fit’. Unlike sildenafil, the mechanism is not particularly straightforward. At that age I mostly used Eastern ‘yoga’ methods for delaying ejaculation although now I think there are also many less unattractive pharmaceuticals that delay ejaculation, though off label, and with less potential side-effects.
Whether there is an actual
interaction between the two compounds though, looks very theoretical to me unless perhaps you mean from long term use? Most of the
clinical studies suggest the opposite, yet I agree it shouldn’t be prescribed readily.
Of course there was a time when they were a lot fussier about prescribing
sildenafil, but then the patent ran out and they accepted that serious side-effects were rare unless there were pre-existing conditions. One could also look at changing prescribing tendencies (for instance) between temazepam and zolpidem, which seemed to be based more on pricing changes and fears of abuse than clinical appropriateness.
Many drugs fail to be licensed or banned on one side of the Atlantic, not on the other and vice versa. Some of the ridiculous decisions have been taken by worried politicians with neither proper debate or understanding of what was involved, even when
the large body of evidence is favourable. As you say, there may not simply be
enough evidence to show a substance is safe (which can be the same as not enough evidence to show that it’s harmful).
But unless we want to discuss the pharmacokinetics it’s all a bit academic on a forum where the interest is “should I take it or not?”
I’m very wary of the nanny state, and will push the boat out on a lot of things (personally, and where I think there’s sufficient evidence). Yet simply on a factual level, for any daft guinea pigs, yes the combination is available, from respected as well as less respected manufacturers, but personally I wouldn’t take it even preference to snorting a line of coke, so other people can make their own mind up!
