CBD may increase the serum concentration and effects of a number of drugs including the following: Antiseizure medications (eg, brivaracetam, carbamazepine, clobazam, topiramate) Immunosuppressants used to prevent rejection after an organ transplant (eg, cyclosporine, tacrolimus) Anticoagulants (eg, warfarin) Tricyclic antidepressants Proton pump inhibitors (eg, omeprazole); diarrhea may occur Nicotine, prolonging duration of action of nicotine Lithium, causing or increasing lithium toxicity Ketamine, possibly enhancing antidepressant effects Methadone Levothyroxine CBD can cause sleepiness and drowsiness, so taking both CBD and sedatives (eg, benzodiazepines, phenobarbital, morphine, alcohol) may make people too drowsy.