Cannabis Interactions with Psychiatric Medications

Introduction to Cannabis-Medication Interactions

The American College of Clinical Pharmacology recommends caution when combining cannabis with psychiatric medications, such as buspirone, lamotrigine, mirtazapine, and brexpiprazole, due to potential pharmacokinetic interactions 1

Cannabis inhibits multiple cytochrome P450 enzymes (CYP3A4, CYP2C19) that metabolize psychiatric medications, potentially increasing their blood levels and adverse effects, requiring dose reduction and close monitoring when used concurrently 1
The National Institute of Mental Health suggests that cannabis-mediated enzyme inhibition affects drug metabolism, increasing medication blood levels unpredictably, particularly because cannabis products have highly variable THC and CBD content 1

The American Psychiatric Association notes that increased buspirone levels may enhance serotonergic effects, theoretically raising serotonin syndrome risk 1, 2
The American Academy of Neurology states that elevated lamotrigine levels increase seizure risk paradoxically, as seen in overdose cases, and cannabis may exacerbate psychiatric disorders in vulnerable individuals, potentially counteracting lamotrigine's mood-stabilizing effects 1
The American College of Clinical Pharmacology recommends that both substances cause sedation through H1 receptor antagonism; combined use compounds drowsiness, dizziness, and confusion 1

The National Institute on Drug Abuse warns that cannabis causes dizziness, confusion, dry mouth, fatigue, tachycardia, orthostatic hypotension, severe confusion, and paranoia, which overlap with side effects from psychiatric medications, particularly sedation and cognitive impairment 1
The American Geriatrics Society notes that older adults face higher risk of confusion, falls, and cardiovascular events (myocardial ischemia/infarction) when combining these substances 1, 3

The American Psychiatric Association states that cannabis use associates with major depression, suicidal ideation, and elevated risk for psychotic disorders 3
The National Institute of Mental Health suggests that patients with pre-existing psychiatric disorders should exercise extreme caution, as cannabis may destabilize their conditions 1

The American College of Clinical Pharmacology recommends starting with the lowest cannabis dose and titrating slowly, monitoring for serotonin syndrome signs, and checking liver function tests when using CBD products, especially at doses >300 mg/day 1, 2
The National Institute on Drug Abuse advises avoiding high-fat meals when taking oral cannabis to prevent excessive absorption 1

The National Highway Traffic Safety Administration warns that cannabis impairs reaction time and coordination for up to 12 hours depending on product type, and drivers testing positive for cannabis are more than twice as likely to be involved in motor vehicle crashes 1, 4
The American Academy of Pediatrics recommends storing cannabis separately from other foods in locked, child-resistant containers out of reach of children and pets, as pediatric cannabis exposures increased from 207 in 2017 to 3,054 in 2021, causing CNS depression, vomiting, and tachycardia 3, 4

The American College of Obstetricians and Gynecologists states that pregnant and breastfeeding individuals must avoid cannabis due to fetal brain development risks and premature birth 3
The American Psychiatric Association notes that patients with history of psychotic disorders should not use cannabis, as it may trigger psychotic episodes 1, 3
The National Institute on Drug Abuse warns that those with substance use disorder history face higher risk of developing cannabis use disorder 4