The stomach secretes HCl in the pH range 1-2.5. I take about 4 different medications. Why don’t they all chemically break down to be useless by the time they leave the stomach?
Because not everything reacts with dilute hydrochloric acid. Some do, so the administered dose is larger to compensate. And some meds have a coating that allows the medicine to survive and pass into the intestines.
Lots of tablets are formulated with HCl as an ingredient. The number of drugs whose chemical names are “blah blah blah HCl” is rather surprising to a layman. This is to get the destruction out of the way during manufacture and make them stomach-compatible. They’re sorta “pre-cooked” from the stomach’s POV.
One might also note that if everything simply broke down into the individual atoms, we wouldn’t get vitamins from our food.
Within the stomach itself, as I understand it, the acid is mostly there to denature proteins so that they unfold into a longer spaghetti that can be broken up by an enzyme called pepsin into smaller peptides.
My guess would be that, since proteins are some of the highest risk things to enter our body - including everything from bacteria and parasites to ingested hormones - a first pass at breaking them down before the rest of the gut is fairly key to our general health.
The stomach is a relatively targeted organ.