Symptoms of vitamin B₁₂ deficiency include abnormal skin color, anemia, mental abnormalities, and indigestion. 1. Abnormal skin color: patients with extensive hyperpigmentation on palms, soles, nails and other parts of the body, and grayish-white hair. 2. Anemia: lack of vitamin B₁₂ can cause megaloblastic anemia, anemic face, hepatosplenomegaly, and skin petechiae in severe cases. It may even induce anemic heart disease and heart failure. 3. Mental abnormality: causing peripheral neuropathy, demyelination changes, manifesting as dementia and coma; it may also lead to reduced sensitivity to the environment, dull expression, etc. 4. Indigestion: manifested as loss of appetite, nausea and vomiting, abdominal pain and diarrhea. If the above symptoms occur, it is recommended to go to the hospital in time for early and regular treatment and medication as prescribed by the doctor.