How do doctors, nurse practitioners, physician associates, pharmacists and patients learn about drug side effects? The most comprehensive source for such data comes from the official prescribing information. This can be found at the DailyMed website of the National LIBRAry of Medicine.

When a new medicine gets approved by the Food Drug Administration, it relies almost exclusively upon the information the drug company gathered during clinical trials. Often, such testing lasts only a few weeks. As a result, some adverse drug reactions go undetected for months, years or even decades.

One of the most important ways we discover these unexpected complications is through voluntary reports from health professionals or patients. To do this, the FDA instituted its MedWatch system in 1993.

If someone experiences a serious unexpected problem while they are taking a prescription or over-the-counter product, they can report this event directly to the FDA by calling 888-463-6332. Online reporting is also available at www.fda.gov/safety/medwatch.

We cannot emphasize enough how critical this FDA service is. A shocking number of dangerous reactions are not revealed during clinical trials for approval. Instead, they are discovered only when a patient suffers an unanticipated, and possibly disastrous, drug complication.

One example involves the oral asthma medicine montelukast (Singulair). The FDA approved this drug in 1998. Within a decade, the agency had received numerous reports of mood changes and suicidal behavior associated with this medicine. Such problems had not shown up during the initial clinical trials.

As a result of voluntary reports to MedWatch, the FDA warned health care professionals and patients in 2009 to be alert to “the potential for neuropsychiatric events with these medications.” A decade later, the agency strengthened its warning, requiring a boxed warning in the prescribing information: “Serious neuropsychiatric (NP) events have been reported with the use of SINGULAIR. The types of events reported were highly variable, and included, but were not limited to, agitation, aggression, depression, sleep disturbances, suicidal thoughts and behavior (including suicide).”

One reader wrote to tell us that Singulair caused her horrible hallucinations. She described “a local teenager who was put on Singulair, suffered altered moods and eventually committed suicide. He had been a happy, normal teen until he took this medication.”

That is just one example of why the FDA’s MedWatch service is so important. Without this reporting system and its database, prescribers and patients would not know about life-threatening adverse reactions that are discovered only after FDA approval.

Sadly, though, the recent firing of many FDA staff is putting this program at risk. That means the MedWatch system may not work as expected.

We have frequently complained about generic drug quality in our columns. Readers alerted us to problems with the generic version of the antidepressant Wellbutrin. When the FDA investigated bupropion, it did so, in part, because of MedWatch reports.

We fear that patients will suffer because of staffing cutbacks. As critical as we have been of the Food and Drug Administration, there is no other organization capable of approving new medicines, monitoring drug safety or detecting food contamination.

In their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email them via their website: www.PeoplesPharmacy.com.