This is wrong.

Acetaminophen is a level 1 (weak) analgesic. Opioids are level 2 or the 3 depending on the drug. Level 3 is the highest level.

https://www.ncbi.nlm.nih.gov/books/NBK554435/

...this isn't very correct

Opioids are certainly considered very potent analgesics because of their interactions with the μ, κ, and δ receptors. These generally work through inducing secondary messengers like cAMP to block calcium channels and activate potassium channels, which usually makes it much more difficult for pain sensing neurons to transmit signals. The underlying pathology of addiction is related to dopamine release in the addiction centers like the VTA, but that's certainly different from how pain is actually blocked.

Tylenol is also not a particularly strong analgesic by any stretch, but it works by inhibiting inflammatory pathways. It's often given in conjunction with opioids because it can reduce swelling and discomfort that isn't strictly pain.

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Well we already know of things that "heighten" pain in more mundane contexts like putting salt or antiseptic cream on a wound, but I don't know if the process is related/similar.

Acting at the local level there are several naturally-produced molecules the potentiate pain. These include prostaglandin, histamine, and leukotriens. With regard to pain thay generally work by lowering the threshold of pain receptors.

That's primarily because opiates themselves have very weak analgesic properties. This is why most prescription opiates come with acetaminophen or APAP, as it is one of the most effective analgesics. What the opiates do however, is dump a ton of dopamine on your neurotransmitters causing you to care less about the pain that you were already in. For some reason after perceiving less pain you'll actually start to feel less pain too, and I don't just mean on the short term there is an actual correlation between accepting the pain and lessening the pain

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The closest answer would be cytokines. These are proteins secreted by the immune system and basically cause inflammation. Some of these cytokines lower the threshold that pain neurons will start to fire at. This is why touching a part of the body that has been hurt is suddenly painful, where applying the same amount of pressure when the body is healthy would not produce the same response.

There's really not a a lot of indications to make these cytokines into drugs, but one, TNF alpha, has been made into a drug to help ramp up the immune system to fight cancer and has "pain" as a side effect. Most non opiate analgesic's block cytokines in one way or another which is how we get pain relief.

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Seratonin is a component of many animal venoms and definitely causes pain. The pain seems to be caused by smooth muscle contraction and not purely a pain enhancement.

https://www.mentalfloss.com/article/68273/serotonin-known-joy-chemical-its-also-found-animal-venom

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Capsaicin (the spicy thing in most hot peppers) causes pain and is used for that purpose in research.

Interestingly, it can also be used to reduce pain.

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