That's right. Absorption is not through the stomach, it is through the small intestine. It is most noticeable when the constipation ends. For hours or even a day or two, I am wondering why I feel so badly over-dosed by the drugs. It's because more of the drug is getting past the stomach and absorbed by the small intestine, and from there, to the brain.

Conversely, block up that drainpipe, with no "movement" in the small intestine, and the drugs are delayed, and get chewed up by acid in the stomach, and I have to take more drugs to get the same "bio-availability" reaching the small intestine.
It is yet one more factor that makes it devilishly hard to balance your drug intake. It's not only a question of how many pills you swallow; it is moreso a question of where they go after you swallow them - how much gets to your neuro system and how fast.
The whole Duodopa schtick is about that: installing a new pipeline to bypass the stomach entirely, and have a steady flow of drugs, and you can speed up or slow down the flow.
But AbbVie charges $60 Grand a year for the product. Would be cheaper if we could balance by bio-availability; the right dosage at the right time. Never get it right, too many factors changing hourly, but keep on trying to balance the dosage.

Next time you feel very under-dosed or over-dosed, think back: when was the last time you used the toilet plunger? Is there a co-relation in timing?

Has the municipality sent you a legal notice about blocking up the town sewage treatment plant? That's always a bad sign.