I've tried them. Here's my report.
Me: I'm over 50, in reasonably good health. Age takes a bit of a toll, and I felt I could use a boost. Sex should be fun, not work, and with age it has started to become more work than I'd like.
Cialis, Viagra, and Levitra all show efficacy. Bottom line: they make it easier to get and keep erections. They do NOTHING for libido - vasodilation is mechanical, so stimulation is still required.
Cialis' effects last longest. The nasty side effects are diminished on day two, but the pill, while advertised as "36 hour" seems to have effect for about 2 days. Your liver is working like a dog to get rid of it the whole time, so there's your tradeoff.
All give me monster headaches the next day (I typically take a dose in the evening). I can't imagine a hangover with a Viagra headache. That would be brutal. A lower dosage seems to reduce (but not eliminate) the headache.
Then there is this weird "blue vision" side-effect. After taking a pill a couple of days in a row this became more noticeable and rather disconcerting. After experiencing this a few times, it was enough to convince me that daily dosing is a bad idea.
Finally, I am convinced that the liver is put under some stress while removing the drug from the system. Blood tests that I've had seem to confirm this. Not enough to push readings outside of "normal" range, but enough to show up on the tests. I take this as another indicator that drinking while taking these pills should be avoided.
I believe the risk of priapism is small. Sexual response may be enhanced, but it is still normal. After ejaculation, the erection subsides like normal. The refractory period may be reduced, but it is still there. If an erection persists, a cold shower should take care of it. The earlier erectile dysfunction drug alprostadil, which is typically injected into the penis, poses a far greater threat of priapism. In fact, it is often prescribed in combination with an antidote drug.
All this said, there are a lot of recreational drugs that will do worse damage than these pills.
I've also tried yohimbe, and that is truly nasty stuff. It is classified by the USDA as a dangerous herb. Risks include racing heartbeat, heart damage, and in extreme cases, death.
Under the best conditions, it is sort of an "upper" - it's impossible to sleep on the stuff - that will increase heart rate and blood pressure, and is psychoactive enough to cause jitters and nervous system discomfort. On the plus side (there is a plus side), yohimbe can increase libido and the sensation is quite remarkable.
The quality of commercial yohimbe is wildly variable, so it's a roll of the dice when you buy it. Experimenting should be done with a small quantity. Strict dietary restrictions should be observed, as yohimbe can cause severe reactions with a number of foods. The "don't ever eat this with yohimbe" list is long: any food that has been aged: processed meats, cheeses, pickled anything, alcohol (yeah, that again), and many others. Restrict diet to fresh fruit and salad, and small portions of freshly cooked meat, with water to drink, for at least four hours before taking yohimbe to minimize the risks. Keep to this diet for 24 hours after taking it.
My own experiments with it (I haven't used it in more than ten years, I am completely done with it, but I did it enough to more-or-less understand it) indicate that the system rapidly builds a tolerance to yohimbe. If you take an equal dose two days in a row, you may not get the effect you're after on the second day. The idea of increasing the dose of this stuff to adjust to a higher tolerance level is too horrible to contemplate. The side-effects are severe, and the risks ramp up with the size of the dose. So, I used it just once a month, maximum. That was enough time to reset tolerance level.
Before you use any of this stuff, learn as much about it as you can. There is plenty of information available on the web.