To alter our behavior or mental processes, a drug must first enter our bloodstream
through ingestion, inhalation, absorption, or injection.
Once in the bloodstream, psychoactive drugs alter our psychological processes
by affecting the nervous system, particularly the synapse.
Then over hours, the influence of the drug gradually wears off
as the liver produces enzymes that metabolize the drug.
An agonist in general increases the effect of neurotransmitters.
Some drugs act as mimics binding and acting like the neurotransmitter, like in the drawing here.
So the drug adds to whatever amount of neurotransmitter is being released.
It is as if more neurotransmitter is being released.
An antagonist does the opposite, reducing the activity at a neurotransmitter.
Some drugs bind but then block the binding of the neurotransmitter, as shown here.
If the neurotransmitter cannot bind, then the neurotransmitter cannot have effect.
Now, let us review some sample drugs.
After the review, you will be asked if the drugs are agonists or antagonists.