Different drugs interact with the bodys cells in different ways. Some drugs affect an area generally, while other pick and choose where to have an analgestic
effect. For example NSAIDs
go for any tissues that experience inflammation while opioids target very specific places on cell membranes called receptors. For drugs that are site specific, such as opioids, actions initiated can be agonist, antagonist or a combination. Agonists are site specific drugs that initiate activity in the cell, triggering activity. Antagonists are another type of drug that act in an opposite way, to block cellular activity. There are also drugs provide a mixture of agonist and antagonist effects.