The majority of drugs either 
There are 7 main drug actions:
*stimulating action through direct receptor agonism and downstream effects
*depressing action through direct receptor agonism and downstream effects (ex.: inverse agonist)
*blocking/antagonizing action (as with silent antagonists), the drug binds the receptor but does not activate it
*stabilizing action, the drug seems to act neither as a stimulant or as a depressant (ex.: some drugs possess receptor activity that allows them to stabilize general receptor activation, like buprenorphine in opioid dependent individuals or aripiprazole in schizophrenia, all depending on the dose and the recipient)
*exchanging/replacing substances or accumulating them to form a reserve (ex.: glycogen storage)
*direct beneficial chemical reaction as in free radical scavenging
*direct harmful chemical reaction which might result in damage or destruction of the cells, through induced toxic or lethal damage (cytotoxicity or irritation)