Cannabinoid (THC) and Tadalafil (Cialis) Interaction
No specific controlled drug-drug interaction study between tetrahydrocannabinol (THC) and tadalafil has been established in labeling or major interaction guidance. [1]
Tadalafil can lower blood pressure through phosphodiesterase-5 (PDE5)–mediated vasodilation. [1]
Cannabis products may increase tadalafil exposure through inhibition of CYP3A4. [2]
Pharmacodynamic Interaction: Blood Pressure Effects
Tadalafil can potentiate the hypotensive effects of vasodilators and agents that lower blood pressure. [1]
Reported adverse effects associated with tadalafil and blood-pressure-lowering contexts include orthostatic signs and symptoms such as dizziness and decreased standing blood pressure. [1]
Substantial alcohol consumption with tadalafil increases orthostatic signs and symptoms. [1]
Pharmacokinetic Interaction: CYP3A4 Metabolism
Tadalafil is metabolized predominantly by CYP3A4. [1]
Coadministration with potent CYP3A4 inhibitors increases tadalafil exposure. [1]
Cannabis inhibits the CYP3A4 pathway. [2]
A CYP3A4-inhibition effect from cannabis products is therefore mechanistically consistent with increased tadalafil exposure. [1], [2]
Clinical Relevance: Expected Adverse Effects
Increased tadalafil exposure from CYP3A4 inhibition can increase the likelihood of tadalafil dose-related adverse effects. [1]
Dose-related adverse effects of tadalafil include blood-pressure–related symptoms such as dizziness. [1]
Situations Requiring Heightened Caution
Concomitant use of tadalafil with nitrates is contraindicated because of marked hypotension risk. [1]
Concomitant use of tadalafil with alpha-blockers requires clinical stability on alpha-blocker therapy prior to tadalafil initiation. [3]
Patients receiving other potent CYP3A4 inhibitors require tadalafil dose limitation. [1]
Practical Medication-Safety Guidance
Avoiding concurrent cannabis use during tadalafil initiation or dose changes reduces uncertainty regarding blood pressure tolerance and potential exposure increases. [1], [2]
If concurrent use occurs, clinical monitoring for dizziness, syncope, and symptomatic hypotension is appropriate given tadalafil’s blood-pressure-lowering potential. [1]
Medication Label References Used for Interaction Risk Assessment
Cialis (tadalafil) labeling identifies CYP3A4 inhibition as a driver of increased tadalafil exposure. [1]
Cialis (tadalafil) labeling identifies tadalafil’s potential to potentiate hypotensive effects in blood-pressure–lowering contexts. [1]
Cannabis pharmacology literature supports CYP3A4 inhibition by cannabis. [2]
Evidence Gaps
A direct THC–tadalafil interaction effect magnitude (e.g., change in tadalafil AUC or Cmax) has not been quantified in the available sources used here. [1], [2]