药物(yào wù) - medication, medicine, drug in Mandarin

药物 (yào wù) is medication considered as a substance: the class of thing, not the packet on the table. It is the word on leaflets, in health reporting and in a doctor's mouth.

In the pharmacy or at home you say 药. 我要买药 is I want to buy some medicine; 我要买药物 sounds like you are placing a wholesale order. The rule of thumb is that 药 counts and 药物 categorises, which is why you hear 吃了三种药 rather than 三种药物 when someone lists what they are on.

The trap for English speakers is drug. 药物 carries none of the recreational sense at all. Illegal drugs are 毒品, literally poison goods, and confusing the two in a sentence about someone's health goes badly wrong very fast.