Drugs can impact the postsynaptic cell by binding directly to the postsynaptic receptors and acting as a blockade, preventing them from being activated by their neurotransmitter.

Drugs effect of blocking receptors postsynaptically

Drugs such as selective receptor agonists bind to specific receptors and activate them, mimicking the natural neurotransmitter at those receptors. these drugs are often very potent, with effects that vary depending on the particular types of receptors activated.

Drugs effect of activating receptors postsynaptically 

Drugs can effects post synaptic events by directly effecting transmitter receptors. This can occur through:
- blockade of receptors
- activation of receptors

Bowdoin College

One way drugs can change synaptic transmission is by modifying the activity of the postsynaptic cell. There are two major classes of postsynaptic drug actions: 
- direct effect on transmitter receptors
- effects on cellular processes within postsynaptic cell

Drugs altering postsynaptic events

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Drugs effects postsynaptically on transmitter receptors 

When they bind to their matching receptor membranes, neurotransmitters can stimulate a variety of changes within the postsynaptic cell. Examples of this include: 
- regualtion of the number of postsynaptic receptors 
- modulation of intracellular signals

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