Today was the first time I've had more than a glass of wine while on Concerta. And that was at night. This was during the day, while Concerta was still working.
Caveat: I can't speak for everyone. The experience must differ somewhat across individuals given their makeup and a variety of other possible contributing and commingling factors. But this is how I felt.
I felt amazing!!! No, I very much did not. Today, while searching for information about the combination of Concerta and alcohol, I ran across several forum posts praising it for its ability to do two things, counteract the downside of alcohol, effects like drowsiness and dizziness, and create euphoria. As an aside, I also learned that methylphenidate (aka Ritalin and Concerta), and ethanol (aka alcohol) combine to produce a similar psychostimulant to methylphenidate called ethylphenidate. I worried about that, but it doesn't seem a big deal, especially given how little I drank.
So, what did I feel? Not much of anything. I briefly felt drowsy and noticed a slight delay in reaction time. But that's about it. After a glass of sangria, maybe 1/4 of a glass of beer, and most of a shot of whiskey (sipped over the course of a couple of hours, mostly because I will never enjoy the taste of alcohol), still no buzz.
But I wasn't disappointed. Based on what little I had read about the combination before today, I expected not to feel that "out of it" sensation of intoxication. I expected to feel lucid. But I didn't expect to feel not the slightest bit intoxicated. That's a first. I can see why people might easily drink too much if they're not paying attention.
And, for this reason, anyone taking Ritalin or Concerta who isn't familiar with how much he or she can safely drink, like teenagers going to their first parties, should really watch it or, preferably, not drink at all. I'm not saying that to be parent-y. I'm saying it for the same reason that you wouldn't punch a brick wall if you couldn't feel pain. You're still hurting yourself.
For me, though, it was just a waste of money. I didn't even feel less inhibited. Lucid and less inhibited would be a cool combo. But nope.
Here is a good summary of the effects of this combination. From what I've read, and this makes the most sense, if you do know your limits and you are going to drink, do it at night, after your medication has worn off. You won't sleep well, but at least you'll know your limit. Otherwise, get ready for a horrendous hangover.