They
are protein in nature and found at the different sites in the cell.
Drug
must interact with the receptor to be able to produce effect.
The
drug receptor complex is similar to the relationship between a
lock-and-key theory. Drug should be structurally compatible to the
receptors or vice versa.
A
single receptor can react with a number of drugs if the drug
conforms to the receptor.
The
intensity of the drug to mediate a response must be proportional to
the number of receptors occupied by the drug.
Drugs
attached to the receptors can be classified as an agonist or
antagonist.
