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🧠 Clinical Overview of Selected Psychoactive Substances
1. Heroin (Diacetylmorphine)
Class: Semi-synthetic opioid, rapidly metabolized to morphine.
⭕️Mechanism: μ-opioid receptor agonist → strong analgesia, euphoria, respiratory depression.
Clinical Concerns:
Rapid CNS penetration → intense addiction potential.
Overdose: respiratory depression, pinpoint pupils, coma (“opioid triad”).
Withdrawal: agitation, mydriasis, rhinorrhea, diarrhea, muscle cramps.
💊Antidote: Naloxone (IV/IM/IN) for acute overdose.
Long-term Risks: HIV, HCV (injection use), collapsed veins, endocarditis.
2. Mephedrone (4-methylmethcathinone, "Meow Meow")
Class: Synthetic cathinone, stimulant (“bath salts”).
⭕️Mechanism: Increases synaptic dopamine, norepinephrine, serotonin (reuptake inhibition + release).
Clinical Concerns:
Acute: euphoria, hyperstimulation, increased sociability.
Toxicity: tachycardia, hypertension, agitation, paranoia, seizures, hyperthermia.
Chronic: neurotoxicity, dependence, psychiatric disorders.
💊No specific antidote → manage supportively (benzodiazepines for agitation/seizures, cooling for hyperthermia).
3. Cocaine
Class: Stimulant, local anesthetic.
⭕️Mechanism: Blocks reuptake of dopamine, norepinephrine, serotonin.
Clinical Concerns:
Acute: intense euphoria, tachycardia, hypertension, mydriasis.
Complications: myocardial infarction (coronary vasospasm), stroke, seizures, sudden death.
Chronic: septal perforation (snorting), psychiatric effects, strong addiction potential.
💊Treatment of Toxicity: Benzodiazepines (for agitation, hypertension), avoid β-blockers (unopposed α-effect).
4. Caffeine
Class: Methylxanthine stimulant.
⭕️Mechanism: Adenosine receptor antagonist → ↑ CNS stimulation, ↑ catecholamines.
Clinical Concerns:
Moderate dose: alertness, reduced fatigue.
High dose: anxiety, tachycardia, insomnia, GI upset.
Toxic dose (>1 g): arrhythmias, seizures.
Withdrawal: Headache, irritability, fatigue.
5. Dopamine (DA)
Class: Endogenous catecholamine.
⭕️Mechanism (dose-dependent):
Low dose: D1 receptor → renal vasodilation.
Moderate dose: β1 receptor → ↑ cardiac contractility.
High dose: α1 receptor → vasoconstriction.
💊Clinical Use: Cardiogenic/septic shock (IV infusion).
Adverse Effects: Tachyarrhythmias, extravasation necrosis (treat with phentolamine).
6. Opioids (general, incl. Morphine, Codeine, Fentanyl)
Class: μ-opioid receptor agonists.
Effects: Analgesia, sedation, respiratory depression, constipation, euphoria.
Clinical Concerns:
Overdose → respiratory arrest.
Dependence & tolerance common.
💊Antidote: Naloxone (short-acting), Naltrexone (maintenance).
Clinical Uses: Pain, anesthesia, palliative care, cough, diarrhea.
7. Adrenaline (Epinephrine)
Class: Endogenous catecholamine, adrenergic agonist.
⭕️Mechanism:
α1 → vasoconstriction, ↑ BP.
β1 → ↑ HR, ↑ contractility.
β2 → bronchodilation.
✅️Clinical Uses:
Anaphylaxis (IM first-line).
Cardiac arrest (IV/IO).
Added to local anesthetics (vasoconstriction).
Adverse Effects: Tachyarrhythmias, hypertension, anxiety, tremor.
🔑 Key Clinical Pearls
Heroin & opioids: respiratory depression is the killer → always think naloxone.
Mephedrone & cocaine: sympathetic storm → benzodiazepines are first-line.
Caffeine: mild compared to others, but toxicity at high doses.
Dopamine & adrenaline: dose-dependent receptor activity → lifesaving in shock/anaphylaxis.
📚 References
Pharmacotherapy Principles and Practice, 6th Edition
American College of Clinical Pharmacy (ACCP) – Toxicology & Critical Care
UpToDate (Opioid toxicity, Cocaine, Synthetic cathinones, Caffeine, Dopamine in shock, Epinephrine)
Lexicomp (Lexi-Drugs Online)
Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 13th Edition
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