common analgesic agent

caffeine is NOT an analgesic.

you've mentioned most of the Common analgesics. others could be ibuprofen and derivatives of salicylic acid (like sodium salt of salicylic acid, for increased solubility).

well, opioid (drugs derived from opium) can be strong analgesics, but the side-effect can be severe. opium, codeine and morphine are examples of these strong analgesics, used under very careful control and in extreme situations (like terminal cancer patients). well.. codeine isn't, as was contained in some old cough syrup.

Nitrous oxide N2O is the common analgesic agent . It is also called laughing or sweet gas . .