Drug side effects are common, and often quite troublesome.

Major side effects, such as severe or even life-threatening allergic reactions, require immediate treatment and discontinuation of the drug. More minor symptoms may be tolerable when weighed against drug benefits. And sometimes, these go away on their own as the body gets used to the drug.

But there’s another type of side effect you hear much less about: ones that are beneficial. Though uncommon, they’re worth keeping in mind when you’re starting a new medicine.

Aren’t all side effects bad?

The term side effect is usually assumed to be a bad thing. And that’s typically true. But that leaves out the “good” side effects. Relatively little is published on this, so it’s not clear how common they are. But four notable examples include:

In the best study I’ve read on the topic, researchers found more than 450 reports of serendipitous beneficial effects of various drugs since 1991. And that may be an underestimation, since report forms did not specifically ask for or label this type of side effect, according to the study authors.

Silver linings: Repurposing and repackaging drugs

While the discovery of helpful drugs can arise unexpectedly, drug developers are increasingly using a more intentional approach: using side effect profiles to look for new uses.

For example:

The availability of large side effect registries has made this method of identifying drugs for repurposing a more realistic option. So, even negative side effects can have a silver lining.

Bad side effects and the nocebo effect

While side effects can be positive, most are not. Medication side effects are a common reason people give for not taking prescribed drugs regularly. And adverse reactions to medicines prompt up to 8% of hospital admissions, according to one analysis.

To make matters worse, in some cases the expectation of side effects seems to make them more likely to occur. Called the nocebo effect, it increases the chances of experiencing a negative side effect and seems due, at least in part, to expectations. Contrast this with the placebo effect, where a sugar pill or another inactive treatment can lead to benefit.

The bottom line

Many people avoid taking medications because they fear possible side effects. That’s understandable. But not taking a medication can mean missing out on its benefits. And anticipation or expectation of side effects can increase the chances you’ll have them.

So, while it’s important to be aware of the most common side effects caused by the medicines you take, it’s also important not to overestimate your chances of experiencing them. And remember: there’s always a chance you’ll have a side effect you actually welcome.

(Robert H. Shmerling, MD, is a senior faculty editor and an Editorial Advisory Board member for Harvard Health Publishing.)

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