Got a bit of knowledge in that department, not enough for credibility tho so Im just sharing my thoughts (in a foreign language, bare with me)

the Sedatives and Analgetics I am Aware of essentially block or slow down the pathway between nerves.

As the Nervous system (divided in two areas: Central NS, the part within your spine and your brain and peripheral NS, all other nerves) uses two one lane streets to work each area (one leading to eg your finger from your brain (motoric) and one the other way around (sensoric) uses transmitters to work.

one could for example try toincrease the production, storage capacity or contact gates of those. That might increase the flat value of sent impulses we interpret as eg pain.

I have to state however that our body has keyholes to those keys all over its body and therefore reacts in most parts of the body to most transmitting agents

(EG adrenaline works the do called "Adrenoceptors" Devided in Alpha1, Alpha2, Beta1 and Beta2 (there seems to be a third pairing Gamma, but as far as I know we havent really understood that one yet). Those are all over our body, so if you inhale Adrenaline to treat eg an anaphylactic shock your lungs will experience the effects first and foremost, but all receptors in your body will take part)

without being capable to explicitly only target the sensoric part of the nervous system the brain would experience an overflow of information, comming from every single nervous cell in our body exposed to the transmitter, wich would probably enforce a reaction similar to an epileptic episode.