Has anyone taken two Viagras at a time? I'm talking about the big pill, the 100 mg. I'm finding it's having less effect these days. I know all about the warnings against that, and that's why I'm asking, if those are just to-be-safe warnings or complete no-goes?
Jesus man, do NOT do that!
Yes, we can develop a tolerance to Viagra (sildenafil) .
Sildenafil is a fast acting hypotensive medication that is directed more at your dick blood supply. But it still has hypotensive effects (lowering blood pressure) overall. That's why people get headaches, blue vision and other side effects like feeling faint or light headed.
While high dosages seldom cause death, it can cause tachycardia (fast heartbeat) that can result in an unstable arrythmia that can lead to a whole slew of known, and unknown adverse effects.
If 100mg isn't getting your dick hard enough, you may well have a serious, underlying cardiovascular issue. Go have a good talk with your GP and get a full cardiac workup. It may very well turn up some latent, developing cardiovascular condition that is better, and easily, treated with medication.
Or you might be fine cardiovascularly and it's all in your head. One way to tell if it is your big head or little head is whether you get good and hard when you jerk off to your fave porn without Viagra.
My Experience
Personally, in my late 30's I started with a 1/4 pill (25mg) when I didn't even need it just to turn White
Pine into White
Oak lumber.

.
As time went on, I bumped to 1/3rd of a pill (33 mg) to get the same effect.
Now I need 1/2 pill (50mg). I say I NEED it because when I fuck with a condom (even magical Skyn Elite Large) I can't maintain good enough wood without Viagra for a good fuck and orgasm.
In real life I go bare because I'm snipped. But I still use 25mg for good measure when I have to please my partner.
When I jerk off, I don't need any medication.
So a LOT of this is an issue of sensitivity and what's in our minds.
I also find that when i am more physically active that I get much better wood and can fuck much better.
I hope the above helps.