Questions: Psychopharmacology Basics

Question 1

A patient takes an opioid pain medication daily for six months following surgery. If the drug is abruptly stopped, she experiences nausea, sweating, and intense pain. Her doctor says she has developed physical dependence. Does this mean she is addicted?

• A. Yes — physical dependence and addiction are the same thing; both involve needing the drug to function normally
• B. Yes — withdrawal symptoms are the defining feature of addiction
• C. No — physical dependence (tolerance + withdrawal) can exist without the compulsive drug-seeking that defines addiction
• D. No — addiction only applies to recreational drugs, not prescribed medications

Answer: (C)

Physical dependence means the body has adapted to the drug's presence such that removal causes withdrawal — a predictable physiological response. Addiction involves compulsive drug-seeking behavior despite negative consequences, involving psychological craving and loss of control. A patient on prescribed opioids who takes them as directed may be physically dependent (tolerance + withdrawal risk) without showing any addictive behavior. Conflating the two leads to undertreating pain patients out of misplaced fear of creating 'addicts.'

Question 2

A researcher is testing a new anti-anxiety compound. At low doses (10 mg) it reduces anxiety. At moderate doses (30 mg) it is maximally effective. At high doses (100 mg) it paradoxically increases anxiety and causes seizures. This pattern is best described as:

• A. A linear dose-response curve, where effect scales proportionally with dose
• B. Evidence of receptor antagonism at high doses
• C. An inverted-U shaped dose-response curve with a narrow therapeutic window
• D. Pharmacokinetic failure — the drug is being cleared too quickly at high doses

Answer: (C)

Many psychoactive drugs produce inverted-U (or biphasic) dose-response curves where moderate doses are most effective, lower doses are subtherapeutic, and higher doses produce diminished or reversed effects. This is not unusual — it often reflects receptor saturation, activation of inhibitory pathways, or off-target effects at high concentrations. The clinical implication is that 'more is better' is false for such drugs; the therapeutic window (range between effective and toxic doses) demands precise dosing. Lithium shows this pattern: narrow window between therapeutic and toxic serum levels.

Question 3

A drug that is highly lipid-soluble will generally cross the blood-brain barrier more readily than a drug that is water-soluble.

• T. True
• F. False

Answer: True

The blood-brain barrier consists of tightly joined endothelial cells with a lipid-rich environment. Passive diffusion across this barrier strongly favors small, lipid-soluble molecules, which can dissolve into and traverse the lipid membranes. Highly water-soluble compounds are largely excluded unless they have specific transport mechanisms. This is why morphine (lipid-soluble) produces rapid CNS effects while many large, polar molecules (like most antibiotics) fail to reach therapeutic concentrations in the CNS despite adequate plasma levels.

Question 4

Tolerance to a drug develops because the drug is metabolized more quickly in the liver over repeated exposures, so less reaches the brain.

• T. True
• F. False

Answer: False

While increased metabolic clearance (metabolic tolerance) can contribute to tolerance in some cases, the primary mechanism described in psychopharmacology is pharmacodynamic tolerance — the brain's neural adaptation to repeated drug exposure. When a drug repeatedly activates receptors, neurons compensate by downregulating receptor density, reducing receptor sensitivity (desensitization), or decreasing neurotransmitter synthesis. The drug reaches the brain in similar concentrations but produces a diminished response because the target system has recalibrated. The withdrawal symptoms when the drug is removed reflect this recalibration.

Question 5

What is the difference between pharmacokinetics and pharmacodynamics, and why do you need both frameworks to understand how a psychoactive drug affects behavior?

Model answer: Pharmacokinetics describes what the body does to the drug — absorption into the bloodstream, distribution to tissues including the brain, metabolism (usually in the liver), and excretion (ADME). Pharmacodynamics describes what the drug does to the brain — its mechanism of action at receptors, transporters, or ion channels. Both are needed because a drug's behavioral effect depends on (1) whether it reaches the brain in sufficient concentration (pharmacokinetics) and (2) what it does once there (pharmacodynamics). A drug with excellent pharmacodynamics but poor CNS penetration may fail entirely; knowing only the mechanism of action tells you nothing about onset, duration, or dosing.

For example, morphine and codeine both act on opioid receptors (similar pharmacodynamics), but codeine must first be metabolized to morphine in the liver before it is active — a pharmacokinetic difference that makes codeine slower-acting and dependent on the CYP2D6 enzyme. Understanding both frameworks is essential for predicting drug effects, dosing intervals, and individual variation in response.