Inclusion Criteria:

1. Males (age range: 5-17yo; inclusive), in treatment with risperidone for ≥ one year.
2. The participants must have two measurements of prolactin ≥ 18.4 ng/ml, obtained within a week.
3. IQ > 35-40 (≥ Moderate intellectual disability).
4. An adult parent/guardian must be available to provide consent and dispense study medication.

Exclusion Criteria:

1. Chronic disorders involving a vital organ (heart, lung, liver, kidney, brain), metabolic diseases (e.g., diabetes, hypo- or hyperparathyroidism, hypo- or hyperthyroidism, growth hormone deficiency), other skeletal diseases (e.g., Paget's disease, osteogenesis imperfecta, rheumatoid arthritis), chronic use of drugs affecting bone metabolism (e.g., corticosteroids), and malnutrition conditions (e.g., chronic diarrhea, inflammatory bowel disease), congenital disorders, or lead poisoning.
2. Participants receiving calcium or multivitamins in the previous three months.
3. A history of renal calculi and fasting random urine calcium/creatinine ratio > 0.2 or any other medical disorder that contraindicates the use of calcium or vitamin D (e.g., hypercalcemic states, hypercoagulability disorders, vitamin D toxicity, malabsorption syndrome, or hypersensitivity to vitamin D products).
4. Laboratory values outside the normal range, except for prolactin, unless the deviations were not clinically significant (e.g. TSH < 10 μIU/ml (76)).
5. Inability to cooperate with the BMD measurements.
6. Bilateral wrist or forearm fractures.
7. Eating disorders.
8. Non-compliance with the prescribed psychiatric treatment as reflected by an undetectable combined risperidone and 9-hydroxy risperidone blood concentration.
9. Plans to move out of State within the next 9 months.