Glucose-6-phosphate dehydrogenase (G6PD) deficiency: People with G6PD deficiency might develop "favism" after eating bitter melon seeds. Favism is a condition named after the fava bean, which is thought to cause "tired blood" (anemia), headache, fever, stomach pain, and coma in certain people. A chemical found in bitter melon seeds is related to chemicals in fava beans. If you have G6PD deficiency, avoid bitter melon.
Surgery: There is a concern that bitter melon might interfere with blood sugar control during and after surgery. Stop using bitter melon at least 2 weeks before a scheduled surgery.