Selective serotonin reuptake inhibitor (SSRI) antidepressants: THC can increase the effect of fluoxetine.

Tricyclic antidepressants: THC can increase the side effects of amitriptyline (i.e. tachycardia, hypertension and sedation).

Nonsteroidal anti-inflammatory drugs (NSAID's): Indomethacin and acetylsalicylic acid (aspirin) reduce the effects of THC.

Barbiturates: These increase the depressive effects of THC and also increase tachycardia associated with THC consumption.

Benzodiazepines: These drugs can increase depression of the nervous system and also of the respiratory system.

Beta-blockers: These reduce tachycardia associated with THC.

Ethanol (alcohol): This can increase nervous system deterioration.

Opiates: Increased sedation and analgesia.

Theophylline: Cannabinoids increase theophylline catabolism. A dosage increase is thus required in such cases.

Anticholinergic agents: Atropine and scopolamine can increase tachycardia produced by THC.

Disulfiram: THC interacts with disulfiram, causing a very unpleasant reaction in the patient. The combination of both substances should therefore be avoided.