5.3 Psychopharmacology of the Major Drug Classes
Key Takeaways
- Physiology and psychopharmacology is one of the nine skill groups NCC AP names for its examinations, so drug classification, intoxication and withdrawal profiles, and the mechanics of tolerance are directly testable content.
- Withdrawal from alcohol and other CNS depressants can be fatal through seizures and delirium tremens, whereas opioid withdrawal is intensely uncomfortable but rarely lethal in otherwise healthy adults — a distinction that drives triage decisions.
- Route of administration governs onset and abuse liability: intravenous and inhaled routes reach the brain in seconds, while oral routes take 20 to 60 minutes, which is why the same drug carries different risk profiles by route.
- Cross-tolerance within a pharmacological class is what allows one drug to substitute for another during withdrawal management, such as a long-acting benzodiazepine for alcohol.
- Half-life predicts withdrawal timing: short-half-life drugs produce early, intense withdrawal, while long-half-life drugs produce delayed, prolonged withdrawal, which is why alprazolam and methadone withdrawal follow very different clocks.
5.3 Psychopharmacology of the Major Drug Classes
NCC AP names physiology and psychopharmacology as one of the nine skill groups its examinations evaluate, and NAADAC's own preparation guidance directs candidates to pharmacology webinars and to the Basics of Addiction module devoted to it. Counselors are not prescribers, but they are expected to recognize what a client is intoxicated on, know which withdrawal syndromes can kill, and understand why the same substance behaves differently when it is smoked rather than swallowed.
This section is organized by pharmacological class, because class membership — not street name or legal schedule — predicts intoxication signs, withdrawal risk, cross-tolerance, and dangerous combinations.
1. The Major Pharmacological Classes
| Class | Representative Substances | Primary Mechanism | Intoxication Presentation | Withdrawal Presentation | Withdrawal Danger |
|---|---|---|---|---|---|
| CNS Depressants (sedative-hypnotics) | Alcohol, benzodiazepines, barbiturates, GHB, "Z-drugs" | Enhance inhibitory GABA-A transmission; alcohol also inhibits NMDA glutamate | Slurred speech, ataxia, disinhibition, nystagmus, impaired memory, sedation, respiratory depression at high dose | Autonomic hyperactivity, tremor, insomnia, anxiety, nausea, hallucinations, seizures, delirium | POTENTIALLY FATAL — seizures and delirium tremens; requires medical withdrawal management |
| Opioids | Heroin, fentanyl, morphine, oxycodone, hydrocodone, methadone, buprenorphine | Mu-opioid receptor agonism | Euphoria then sedation, pinpoint pupils, itching, constipation, slowed respiration, "nodding" | Dilated pupils, lacrimation, rhinorrhea, yawning, piloerection, myalgia, abdominal cramping, diarrhea, vomiting, intense craving | Rarely fatal in healthy adults, but dangerous with dehydration, in pregnancy, and because of overdose risk after tolerance loss |
| Stimulants | Cocaine, methamphetamine, amphetamine salts, methylphenidate, cathinones | Increase synaptic dopamine and norepinephrine (reuptake blockade or reversal of transport) | Euphoria, hypervigilance, grandiosity, pressured speech, dilated pupils, tachycardia, hypertension, hyperthermia, paranoia, formication | "Crash": profound dysphoria, hypersomnia, hyperphagia, psychomotor slowing, vivid dysphoric dreams, intense craving, suicidal ideation | Not physiologically lethal, but the depressive crash carries real suicide risk requiring assessment |
| Cannabinoids | Cannabis, concentrates, synthetic cannabinoids ("K2," "Spice") | CB1 receptor agonism (synthetics are full agonists and far more potent) | Conjunctival injection, increased appetite, tachycardia, altered time perception, impaired short-term memory, anxiety or paranoia at high potency | Irritability, anger, anxiety, sleep disturbance with vivid dreams, decreased appetite, restlessness, physical discomfort (a DSM-5 diagnosis) | Not dangerous, but frequently underestimated by clients and clinicians; synthetic cannabinoids can cause seizures, agitation, and death |
| Hallucinogens | LSD, psilocybin, mescaline, DMT | Primarily 5-HT2A serotonin agonism | Perceptual distortion with generally intact reality testing, synesthesia, dilated pupils, emotional lability, possible panic | No characteristic physiological withdrawal syndrome | Risk is behavioral — panic reaction, injury, hallucinogen persisting perception disorder |
| Dissociatives | PCP, ketamine, dextromethorphan, nitrous oxide | NMDA receptor antagonism | Nystagmus (classically vertical with PCP), dissociation, analgesia, agitation, unpredictable violence, ataxia, blank stare | Mild; craving and dysphoria | Behavioral danger during intoxication is the primary risk; nitrous causes B12 inactivation and neuropathy |
| Inhalants | Toluene-based solvents, glue, paint thinner, aerosols, nitrites | Varied, largely nonspecific membrane and GABA effects | Rapid brief intoxication, dizziness, slurred speech, euphoria, chemical odor, perioral rash ("glue sniffer's rash") | Mild and inconsistent | Sudden sniffing death syndrome from cardiac arrhythmia can occur on any exposure, including the first |
| Nicotine | Cigarettes, vaping products, smokeless tobacco | Nicotinic acetylcholine receptor agonism | Mild stimulation, appetite suppression | Irritability, anxiety, difficulty concentrating, increased appetite, craving, dysphoria | Not dangerous, but the leading preventable cause of death among people in SUD treatment |
| Anabolic-androgenic steroids | Testosterone esters, nandrolone, stanozolol | Androgen receptor agonism | Not classically euphoric; irritability, aggression, mood lability | Depression, fatigue, loss of libido; depression can be severe | Withdrawal depression carries suicide risk |
[!IMPORTANT] The rule that decides triage. Ask first: is this a CNS depressant? Withdrawal from alcohol, benzodiazepines, and barbiturates can kill through seizures and delirium tremens and requires medical management. Opioid withdrawal feels catastrophic to the client and looks dramatic, but is rarely lethal in a healthy adult. Candidates who reverse these two facts choose the wrong level of care on vignette items — and, in practice, send the wrong person home.
2. Route, Onset, and Abuse Liability
The faster a drug reaches the brain, the more intense the reinforcement and the higher the abuse liability. The same molecule can be a moderate-risk medication by one route and a high-risk drug by another.
| Route | Approximate Time to CNS Effect | Notes |
|---|---|---|
| Intravenous | 5 to 20 seconds | Highest abuse liability; infection, endocarditis, abscess, and bloodborne virus risk |
| Inhalation / smoking | 7 to 10 seconds | Effectively as fast as IV; drives crack cocaine and methamphetamine use patterns; pulmonary damage |
| Intranasal (snorting) | 3 to 5 minutes | Nasal septum damage with chronic use |
| Sublingual / buccal | 5 to 15 minutes | Bypasses first-pass metabolism; the buprenorphine route |
| Oral | 20 to 60 minutes | Slowest onset, lowest abuse liability, subject to first-pass hepatic metabolism |
| Transdermal | Hours | Fentanyl patches; diversion by chewing or extraction is a well-known lethal risk |
3. Half-Life, Potency, and the Shape of Withdrawal
Half-life is the time for plasma concentration to fall by half, and it sets the clock for withdrawal:
- Short half-life leads to early, intense withdrawal. Alprazolam, heroin, and short-acting alcohol effects produce withdrawal within hours, sharply peaked.
- Long half-life leads to delayed, prolonged, milder-per-day withdrawal. Diazepam, methadone, and chlordiazepoxide produce withdrawal that may not begin for one to three days and can last weeks.
This is why withdrawal management often substitutes a long-acting agent within the same class — chlordiazepoxide or diazepam for alcohol, methadone or buprenorphine for short-acting opioids — and then tapers it. The substitution works because of cross-tolerance.
Rough withdrawal timelines to know:
| Substance | Onset | Peak | Duration |
|---|---|---|---|
| Alcohol | 6 to 24 hours | 24 to 72 hours (seizure risk 12 to 48 hours; delirium tremens typically 48 to 96 hours) | 5 to 7 days for acute phase |
| Short-acting opioids (heroin) | 8 to 12 hours | 36 to 72 hours | 4 to 7 days |
| Methadone | 24 to 48 hours | 3 to 8 days | 2 to 3 weeks or longer |
| Short-acting benzodiazepines | 1 to 2 days | 2 to 4 days | 2 to 4 weeks, with protracted symptoms possible |
| Long-acting benzodiazepines | 2 to 7 days | 1 to 2 weeks | Weeks to months |
| Stimulants | Hours | 2 to 4 days | 1 to 2 weeks of anhedonia and craving |
Post-acute withdrawal. After the acute syndrome resolves, many clients experience weeks to months of sleep disturbance, mood instability, cognitive fog, and craving surges. Normalizing this — and warning the client it is coming — prevents the interpretation "the treatment isn't working" that so often precedes a return to use.
4. Tolerance and Its Relatives
| Term | Definition | Clinical Illustration |
|---|---|---|
| Tolerance | Diminished response to the same dose, or the need for more to achieve the same effect | A DSM-5-TR criterion; the client who now needs a fifth of vodka to feel what a pint once produced |
| Metabolic (pharmacokinetic) tolerance | Liver enzyme induction speeds drug clearance | Chronic alcohol use inducing CYP2E1 |
| Cellular (pharmacodynamic) tolerance | Receptor downregulation and adaptation | Mu-opioid receptor adaptation |
| Behavioral tolerance | Learned compensation for impairment | The experienced drinker who can walk a straight line at a blood alcohol level that would floor a novice |
| Acute tolerance (tachyphylaxis) | Tolerance developing within a single episode of use | Greater impairment on the ascending than the descending limb of the blood alcohol curve |
| Reverse tolerance (sensitization) | Increased response to the same dose over time | Stimulant-induced psychosis emerging at doses previously tolerated; advanced liver disease lowering alcohol tolerance |
| Cross-tolerance | Tolerance to one drug conferring tolerance to another in the same class | Why a benzodiazepine can substitute for alcohol in withdrawal management |
| Cross-dependence | One drug can suppress withdrawal from another in the same class | The pharmacological basis of methadone and buprenorphine maintenance |
Drug interactions that kill:
- Additive / synergistic depression. Alcohol plus benzodiazepines plus opioids — all three depress respiration, and combinations account for a large share of overdose deaths. The opioid-plus-benzodiazepine combination is the one most often tested.
- Potentiation. One drug amplifies another's effect beyond simple addition.
- Antagonism. One drug blocks another — the therapeutic mechanism of naloxone and naltrexone, and the reason naltrexone precipitates violent withdrawal in an opioid-dependent person.
- Speedball patterns. Combining a stimulant with an opioid masks the sedative warning signs of opioid overdose while the stimulant wears off first, leaving unopposed respiratory depression.
[!NOTE] Counselor scope. Recognizing these patterns is squarely within a counselor's role; adjusting medications is not. The correct action on an examination item is to report objective observations to the medical team or refer for medical evaluation, not to advise the client about dosing. See Section 13.5 on scope of practice.
A client presents to an outpatient intake reporting daily consumption of a liter of vodka plus 6 mg of alprazolam for the past two years, with last use approximately 10 hours ago. The client is tremulous, diaphoretic, hypertensive, and mildly disoriented. Which understanding of the pharmacology should drive the counselor's immediate action?
A client in an opioid treatment program asks why the physician switched him from heroin to methadone rather than simply having him stop, and why the program can substitute one opioid for another at all. Which pharmacological concept explains this?
Which statement about route of administration and abuse liability is accurate and clinically useful in assessment?