They're studied in patients who are highly screened for eligibility and are carefully monitored. After a drug is out on the market, patients will usually not be as rigorously studied or monitored. And, yes, in the general practice of medicine, drugs are used for conditions other than those they were approved for. We must take all of these factors into account as we work with sponsors to try to make safe and effective products available to patients as quickly as possible. Unlike in other areas of FDA's work, there is no set formula or standard for a determination that a product is safe.
Safety is a relative term.
There is a continuum of uncertainty that is tolerated, depending on the seriousness of the illness. Every single drug has side effects. Sometimes these will be rare, and sometimes these will not be very serious. But for every drug that we approve, we have to balance the benefits of the drug against its risks. We need to make clear what the risks are, and communicate that information as effectively as possible to all involved.