A bevy of reasons, there could be a batch recall or the shipment itself might be spoiled. The manufacturers may be unable to get the ingredients. The drug may be high in demand and not able to meet supply needs or a manufacturer might be waiting to accumulate a large enough order on this item(s) to match profit with production/shipping costs. There could also be a cost issue causing friction with obtaining the drug from the manufacturer as well. In any case, talk to your doctor! Do not delay; there are usually other options that can be utilized.