I don't know much about how stomach acidity and other biological factors can effect the breakdown of XR pills, but say if when people are especially stressed/in pain/etc, they tend to secrete more of a certain hormone/chemical that could be found in the stomach, as well as probably throughout the body/
XR pills are basically instant release pills that last too long. If XR pills were designed so that their tendency to dissolve is only in acidic environments in reaction to stress/pain hormones that the body secretes. Then you would only need to take one pill a day, it would last all day long because it wouldn't be constantly dissolving, it would only kick in when you really need it (when your body is signaling that you're actively stressed/in pain). One XR pill might even last 2 or 3 days if you're having a particularly relaxed week. It would probably be difficult to abuse, and their wouldn't be recreational effects regardless of what dose you take orally, only your pill releasing a little bit of its contents when you actually need it.