Acute and chronic effects, including overdose, from the use of - cannabis

Description

Cannabis (THC = psychoactive, CBD = non-intoxicating, may modulate THC effects)
Acute: euphoria, relaxation, altered perception, tachycardia, conjunctival injection, dry mouth, impaired coordination/memory; high dose -> anxiety, panic, cannabinoid hyperemesis syndrome (chronic heavy use)
Chronic: dependence (less severe than opioids/stimulants but real), amotivational features, respiratory symptoms if smoked, psychosis risk in vulnerable individuals

Most commonly used illicit drug in Australia
Increasing potency of available THC-dominant products over recent decades
Legal/medicinal cannabis prescribing has expanded - relevant to distinguishing therapeutic from recreational use in history-taking

THC - partial agonist at CB1 receptors (CNS) -> dopaminergic/GABAergic modulation -> the intoxicating effects
Cannabinoid hyperemesis syndrome: paradoxical - chronic heavy use -> cyclical vomiting, relieved characteristically by hot showers/bathing
Psychosis association: strongest with high-THC, low-CBD products, early age of first use, and genetic vulnerability (e.g. family history of psychosis)

Clinical + urine drug screen (THC metabolites detectable for weeks in chronic heavy users - not a marker of recent/current impairment)
Cannabinoid hyperemesis - diagnosis of exclusion in a chronic heavy user with cyclical vomiting + relief with hot showers; other causes of vomiting must be excluded
Assess for psychotic symptoms with any heavy use, especially in adolescents/young adults

Acute

Supportive - reassurance for anxiety/panic ("talk down"), benzodiazepines if severe
Cannabinoid hyperemesis - supportive antiemetics (often poorly responsive to standard antiemetics), topical capsaicin cream can help, hot showers, cessation of cannabis is the definitive treatment

Chronic/dependence

Psychosocial interventions (CBT, motivational interviewing) - no approved pharmacotherapy for cannabis dependence
Screen for and manage psychiatric comorbidity

Psychosis/schizophrenia - strongest evidence of any illicit drug for a causal contribution in vulnerable individuals
Anxiety and depression
Respiratory symptoms (chronic bronchitis) if smoked, though weaker lung cancer association than tobacco

Withdrawal syndrome (irritability, insomnia, dec appetite, craving) is real but milder than opioid/alcohol withdrawal, peaks day 2-6
Cannabinoid hyperemesis resolves with sustained cessation, often not recognised until cannabis is stopped and symptoms remit

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