Chapter 5: Psychopharmacology

5.1: Introduction

Psychopharmacology, the study of how drugs affect the brain and behavior, is a relatively new science, although people have probably been taking drugs to change how they feel from early in human history (consider the eating of fermented fruit, ancient beer recipes, and chewing on the leaves of the cocaine plant for stimulant properties as examples). The word psychopharmacology itself tells us that this is a field that bridges our understanding of behavior (and brain) and pharmacology, and the range of topics included within this field is extremely broad.


Image showing communication between neurons in the brain
Figure 1. Drugs that alter our feelings and behavior do so by affecting the communication between neurons in the brain.

Virtually any drug that changes the way you feel does this by altering how neurons communicate with each other. Neurons (86 billion in your nervous system) communicate with each other by releasing a chemical (neurotransmitter) across a tiny space between two neurons (the synapse). When the neurotransmitter crosses the synapse, it binds to a postsynaptic receptor (protein) on the receiving neuron, and the message may then be transmitted onward. Obviously, neurotransmission is far more complicated than this—we reviewed neurotransmission in a previous chapter, and links at the end of this chapter can provide some useful additional background information—but the first step is understanding that virtually all psychoactive drugs interfere with or alter how neurons communicate with each other.

There are many neurotransmitters. Some of the most important in terms of psychopharmacological treatment and drugs of abuse are outlined in Table 1. The neurons that release these neurotransmitters, for the most part, are localized within specific circuits of the brain that mediate these behaviors. Psychoactive drugs can either increase activity at the synapse (these are called agonists) or reduce activity at the synapse (antagonists). Different drugs do this by different mechanisms, and some examples of agonists and antagonists are presented in Table 2. For each example, the drug’s trade name, which is the name of the drug provided by the drug company, and generic name (in parentheses) are provided.


Table 1. How neurotransmitters affect behaviors or diseases
Neurotransmitter Abbreviation Behaviors of Diseases Related to These Neurotransmitter
Acetylcholine ACh Learning and memory; Alzheimer’s disease’ muscle movement in the peripheral nervous system
Dopamine DA Reward circuits; Motor circuits involved in Parkinson’s disease; Schizophrenia
Norepinephrine NE Arousal; Depression
Serotonin SHT Depression; Aggression; Schizophrenia
Glutamate GLU Learning; Major excitatory neurotransmitter in the brain
GABA GABA Anxiety disorders; Epilepsy; Major inhibitory neurotransmitter in the brain
Endogenous Opiods Endorphins, Enkephalins Pain; Analgesia; Reward

A very useful link at the end of this chapter shows the various steps involved in neurotransmission and some ways drugs can alter this.

Table 2 provides examples of drugs and their primary mechanism of action, but it is very important to realize that drugs also have effects on other neurotransmitters. This contributes to the kinds of side effects that are observed when someone takes a particular drug. The reality is that no drugs currently available work exactly where we would like them to be in the brain or only on a specific neurotransmitter. In many cases, individuals are sometimes prescribed one psychotropic drug but then may also have to take additional drugs to reduce the side effects caused by the initial drug. Sometimes individuals stop taking medication because the side effects can be so profound.


Table 2. Examples of drugs, their primary mechanism of action, use, and whether agonists (increase activity at the synapse) or antagonists (reduce activity at the synapse).
Drug Mechanism Use Agonist/Antagonist
L-dopa Increase Synthesis of DA Parkinson’s disease Agonist for DA
Adderall (mixed salts amphetamine) Increase Synthesis of DA, NE ADHD Agonist for DA, NE
Ritalin (methylphenidate) Blocks removal of DA, NE and lesser (5HT) from synapse ADHD Agonist for DA, NE mostly
Aricept (donepezil) Blocks removal of ACh from synapse Alzheimer’s disease Agonist for ACh
Prozac (fluoxetine) Blocks removal of 5HT from synapse Depression, obsessive compulsive disorder Agonist 5HT
Seroquel (quetiapine) Blocks DA and 5HT receptors Schizophrenia, bipolar disorder Antagonist for DA, 5HT
Revia (naltrexone) Blocks opiod post-synaptic receptors Alcoholism, opiod addiction Antagonist (for opioids)

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