Lithium has a relatively narrow therapeutic range. As a result of drug-drug interactions, the blood level of lithium is highly affected. This case describes lithium toxicity and its management resulting from drug interactions with lithium. A 37-year-old woman with bipolar illness, essential hypertension, hypothyroidism, unipolar depression, and schizoaffective disorder was admitted to the emergency department with hand numbness, tremor, agitation, and tachycardia. When the patient's lithium blood level was 1.7 mmol/L, lithium treatment was discontinued, and he was hospitalized in the intensive care unit with a prediagnosis of lithium toxicity. The clinical pharmacist used the Lexicomp drug interaction database to examine interactions. Candesartan, hydrochlorothiazide and dexketoprofen were determined to be the cause of toxicity. The clinical pharmacist advised amlodipine as an antihypertensive because it did not interact, reducing lithium levels to 1.4-1.2 and 0.8 mmol/L. Lithium toxicity due to drug-drug interactions was resolved by clinical pharmacist intervention.