How long does vitamin AD take to be effective is related to the individual’s physical condition, ranging from 1 to 3 months. Vitamin AD can promote the absorption of calcium, mainly for the treatment of rickets and vitamin AD deficiency caused by night blindness, chondromalacia, taking this drug. It takes a period of time to have some effect. If the individual physique is good absorption fast, generally take about 1 month will appear obvious therapeutic effect. If the elderly slow absorption at least 2 ~ 3 months to be effective. During the period of taking the drug should be more sunshine to promote the absorption of the drug, but this drug is not recommended for long-term consumption, if long-term use may cause chronic poisoning, such as joint pain, swelling, nausea, vomiting, headache, constipation and other phenomena. It is contraindicated for those who are allergic to this product. Therefore, it is best to take vitamin AD under the guidance of a doctor, and when the disease gets better, you can stop using it.