Have you ever searched for information about the side effects of a medication? These days, most people put the name of their drug into a search engine along with the phrase “side effects.” Whatever comes up is assumed to be an authoritative answer.

Such searches are often incomplete. Now that artificial intelligence is the initial response, many people don’t get further than the first paragraph. Even if they do dig deeper, some databases do not give any information about the frequency of a side effect.

What most people see are categories such as “common” or “serious” side effects. That is not very informative. For example, the popular weight loss medicine semaglutide (Wegovy) has a long list of “common” side effects: “nausea, diarrhea, vomiting, constipation, stomach pain, headache, fatigue, indigestion, dizziness, gas, heartburn or runny nose.”

Reading such a long list provides little detail, though some databases offer more detailed information. The average patient may find this offers little real guidance.

Most people do not realize that drug companies are the primary source for such side effect data. The manufacturers collect this information during clinical trials prior to Food and Drug Administration approval. Such studies are often short-term. Side effects that only show up after many months or years will rarely be detected during initial testing.

Side effect data may be a response to questions asked by the people running the clinical trials. How they are framed can profoundly influence the answers.

For example, the first injectable form of semaglutide approved by the FDA was to treat diabetes. The drug was Ozempic. The weekly dose ranges from 0.5 milligrams to 2 milligrams.

The same identical semaglutide drug was approved a few years later for weight loss under the name Wegovy.

The weekly dose ranges from 0.25 milligrams to 2.4 milligrams.

The official prescribing information based on clinical trial data lists diarrhea as a side effect in 8.8% of patients taking a 1-milligram dose of Ozempic and 22% to 30% for a 2.4 milligram dose of Wegovy. The wide difference in side effects might not seem strange since the dose of semaglutide was more than double in the Wegovy trial.

But here is where it gets interesting. These clinical trials require placebo arms. That means a group of similar patients unknowingly injects an inert liquid instead of semaglutide.

Volunteers in the Ozempic trial who were getting placebo injections reported diarrhea 1.9% of the time. Subjects in the Wegovy trials getting placebo injections reported diarrhea 16% to 19% of the time. That’s a 10-fold difference in diarrhea symptoms on an inert placebo injection. The FDA can’t explain this oddity.

Even more confusing, the official prescribing information for Wegovy warns doctors to “Monitor patients treated with Wegovy for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior.” There is no such precaution for the identical drug Ozempic. Australia has just issued a warning about depression for both Ozempic and Wegovy, but the FDA has not followed suit.

Such discrepancies make it hard for physicians and patients to know the true incidence of side effects. Until we have a better system, patients will need to pay attention to their own bodies. Any unusual symptoms should be brought to the prescriber’s attention.

In their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of King Features, 300 W. 57th Street, 41st Floor, New York, NY 10019, or email them via their website: www.PeoplesPharmacy.com. Their newest book is “Top Screwups Doctors Make and How to Avoid Them.”