Introduction: In patients with medication for chronic illnesses, using medications for chronic illnesses, the doses of drugs should be adjusted before bariatric surgery. Studies investigating the pharmacokinetics of the oral drugs used after bariatric surgery are limited. We will present a young bipolar male obese patient who should continue to use lithium after bariatric surgery. Case: Twenty-six-year-old male was applied to our clinics with the complaint of weight gain of 20 kg in a year. This patient was reported to have taken risperidone 2 mg tb 1x1 and lithium capsule 1x3 due to bipolar disorder (BPD). Also, the patient who had previously been diagnosed with asthma did not take any inhaler medication for it. On physical examination; body weight was 195 kg, height 184 cm, body mass index 57.5 kg/m2 and vital findings were stable. Respiratory examination revealed rhonchus, and the examination of other organ systems was unremarkable. Laboratory evaluation revealed that glucose was 480 mg/dL, creatinine: 0.9 mg/dL, ALT: 65 U/L, AST: 28 U/L, Na: 143 mmol/L, K: 4 mmol/L, HDL: 26 mg/dL, LDL: 165 mg/dL, Triglyceride: 200 mg/dL, HbA1c: 8.5%.With the diagnosis of type 2 diabetes, exenatide 5 mcg 2x1 subcutaneous and metformin 1000 mg 2x1 tb were given, and hyperglycemia was regulated.The patient was examined by psychiatry, and BPD was found to be stable. Serum level of lithium was 0.5 mEq/L. Laparoscopic Roux-n-Y gastric bypass (RYGB) surgery was planned after bariatric surgery council. To decrease postoperative pulmonary complications, perioperative inhaler beta2 agonist was given. Metformin and exenatide was discontinued after RYGB. The patient was given bariatric surgery diet, but he could not tolerate oral lithium or risperidone. Sublingual olanzapin 10 mg was given. Later, in postoperative 1st month, risperidon im 25 mg each 2 weeks was initiated to be taken in every 2 weeks. Because of intolerance, it was not given until postoperative 6th month. Lithium capsule 1x1 was started at postoperative 6th month, and increased gradually up to 1x3 capsule. The level of lithium was 0.21 and 0.129 mEq/L, in the first and 6th month of the initiation of lithium, respectively. Effective level could not be achieved. Conclusion: Due to nausea, postoperative use of lithium may become difficult. Lithium could be given to our patient regularly after 6th postoperative month, but the reference level could not be achieved. Large studies investigating the use of lithium in patients with BPD after bariatric surgery will clarify this issue.