system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do high blood pressure medicines help reduce blood pressure?
gpt
Couple of ways. High blood pressure mostly comes down to the heart pumping harder/faster, blood vessels squeezing harder (blood vessels have a little lining of muscle), and salt/water balance. The body controls all this in a couple of complicated ways.

Let's cover the most common groups:

* Calcium channel blockers (like amlodipine) stop blood vessels from squeezing down as tight by working on that little lining of muscle.

* ACE inhibitors (like lisinopril) stop part of a signal relay that normally tells blood vessels to squeeze down and tells the kidneys to hold on to salt and water. Angiotensin receptor blockers (ARBs, like losartan) are really similar, but work on a different part of that relay.

* Thiazide diuretics (like HCTZ) are interesting. You'll mostly read that they make you pee off salt and water, so you have less blood in your vessels, meaning lower blood pressure. There actually seems to be a lot more to it long-term, but it's not ELI5 (they don't even explain this part well in med school.)

* Beta-blockers (like metoprolol) block signals that tell the heart to beat harder and faster.

* Alpha-blockers (like prazosin) block signals that tell blood vessels to squeeze down. They act on a different part of the same big system as beta-blockers. 

* Central alpha agonists (like clonidine) act on the same system as alpha and beta-blockers, but instead of blocking the signal, they trick the brain into not putting it out to begin with.

In general, what we've realized is that blood pressure isn't always the thing to focus on. Some drugs that decrease blood pressure don't make you live any longer, or have fewer heart attacks and strokes. (Alpha and beta blockers are both great for a lot of other problems, but not great if high blood pressure is the only one. Thiazides, calcium channel blockers, ACE inhibitors and ARBs are all cool.)