About six or seven weeks ago, I rediscovered a package of Cosmic Caramels tucked away in the refrigerator that had basically been sitting there for 2½ years. They worked just like they originally did; same effects, same strength, the whole bit. I’ve been slicing off pieces of the last caramel every week or so, as part of my general strain rotation.
The other day, I did the same thing, but suddenly nothing happened (or at least, almost too little to measure). The reliable little chunk I had been lopping off the end, which brought me to a cheery [4.5], was now giving me a mediocre and somewhat melancholy [1.5]. I put it down to a glitch, but then thought about it and tried a piece twice as big, which gave out with a half-hearted . WTF?
So today, I took a look at the last remaining chunk, which was comparatively huge. At the rate the effects seemed to be deteriorating, I thought it was safe to eat the whole thing, even though a piece this size would usually be good for taking my whole family to visit the moon with me. I did notice (but forgot to take a picture of, dammit), that the caramel showed signs of sugar recrystallization (hard spots) in places, but looked otherwise just fine.
Well, I was right: I didn’t hallucinate or even get very high (maybe  or so). But I had the most peculiar fuzzy-headed feeling, and took a 2-hour nap. This is something I literally haven’t done in at least six months, and used to do all the time until 2011 (about six months after I started on MMJ).
My working hypothesis at this point is that opening and using this last piece exposed it to enough air that it started breaking down, and the process is not gradual but tends to happen all at once.
I’m pretty sure that most bud deteriorates fairly consistently (THC turns to CBN) over time, but this was an edible, so I’m guessing that it has to do with the food itself. As a control, I happen to have some other identical caramels that have been in the freezer all this time. I’ll be defrosting them one at a time for more experiments. Any volunteers? :-)