| Drug Interactions | Effect |
| Antipsychotics |
| Alcohol | Intensifies CNS depression |
| Amphetamines | Antagonizes efficacy |
| Antacids | Decreases neuroleptic absorption |
| Anticholinergics | Additive anticholinergic effects |
| Antihypertensivesa | Hypotension |
| Barbiturates | Decreases neuroleptic levels |
| Epinephrinea | Hypotension |
| Levodopa | Antagonizes levodopa efficacy |
| Lithium | Increases neurotoxicity |
| MAOIsa | Hypotension |
| TCAs | Increases TCA plasma levels |
| BZs |
| Alcohol (and other CNS depressants) | Intensifies CNS depression |
| Alcohol (acute) | Increases BZ levels |
| Alcohol (chronic) | Decreases BZ levels |
| Antacids | Decreases BZ levels |
| Cimetidineb | Increases BZ levels |
| Disulfiramb | Increases BZ levels |
| SSRIs | Increases BZ levels |
| Isoniazidb | Increases BZ levels |
| Oral contraceptivesb | Increases BZ levels |
| Rifampinb | Decreases BZ levels |
| Tobacco/nicotineb | Decreases BZ levels |
| Carbamazepine (induces CYP450 3A3/3A4) |
| Alprazolam | Decreases alprazolam levels |
| Cimetidine | Increases carbamazepine levels |
| Clonazepam | Decreases clonazepam levels |
| Diltiazem, verapamil | Increases carbamazepine levels |
| Erythromycin | Increases carbamazepine levels |
| Isoniazid | Increases carbamazepine levels |
| Phenobarbital | Decreases carbamazepine levels |
| Phenytoin | Decreases carbamazepine levels |
| Primidone | Decreases carbamazepine levels |
| Propoxyphene | Increases carbamazepine levels |
| SSRIs | Increases carbamazepine levels |
| Valproate | Decreases valproate levels |
| Lithium |
| Acetazolamide | Decreases lithium levels |
| Antipsychotics | Increases neurotoxicity |
| Beta-blockers | Decreases tremor |
| Carbamazepine | Increases lithium effects |
| Captopril, enalapril | Increases lithium levels |
| Cyclosporine | Markedly increases lithium levels |
| Diltiazem, verapamil | Increases lithium toxicity |
| Methyldopa | Increases lithium toxicity |
| Potassium iodide | Enhances hypothyroid effects |
| Tetracycline | Increases lithium levels |
| Thiazide diuretics | Increases lithium levels |
| SSRIs |
| BZsb | Increases BZ levels |
| Carbamazepine | Increases carbamazepine levels |
| Antipsychotics | Increases neuroleptic levels |
| TCAs | Increases TCA levels |
| MAOIs |
| Alcohol | Additive CNS depression |
| Clomipramine | Serotonin syndrome |
| SSRIs | Serotonin syndrome |
| Meperidine | Serotonin syndrome |
| Phenothiazine | Hypotension |
| Succinylcholine | Prolongs muscle relaxation |
| Tyramine | Potential hypertensive crisis |
| Sympathomimetic drugs (amphetamine, cocaine, dopamine, ephedrine, epinephrine, metaraminol, norepinephrine, phenylpropanolamine, phenylephrine) | Potential hypertensive crisis |
| TCAs |
| Alcohol | Additive CNS depression |
| Anticholinergics | Additive anticholinergic effects |
| Antihypertensives (guanethidine, clonidine, debrisoquin) | Increases hypertension |
| Antipsychotics | Increases TCA plasma levels |
| BZs | Additive CNS depression |
| Class I antiarrhythmics (disopyramide, lidocaine, quinidine, procainamide) | Prolongs cardiac conduction |
| Liothyronine | Enhances antidepressant action |
| CNS=central nervous system; MAOI=monoamine oxidase inhibitor; TCA=tricyclic antidepressant; BZ=benzodiazepine; SSRI=selective serotonin reuptake inhibitor; CYP450=cytochrome P450 |
| a Phenothiazines (chlorpromazine, thioridazine, and mesoridazine) |
| b Except oxazepam, lorazepam, alprazolam, and temazepam |
| Source: Rundell JR, Wise MG: Concise Guide to Consultation Psychiatry, 3rd ed, Washington, DC, American Psychiatric Press, 2000, pp 176—178 |