This isn’t that strange in the context that all medicines, while generally safe in OTC form, can have negative side effects if used for too long or at the wrong dose or in the wrong circumstance.

My wife has one kidney and as such is told to avoid NSAIDs as a class of medicine. She’s realistically fine taking it every so often but her doctors are asking her to avoid using kidney capacity that could hypothetically be needed to filter and excrete something else.

Acetaminophen/Paracetamol is great alternative for her since it’s processed in the liver. However if you’re a frequent drinker, have a liver deficiency, or have to take some other drug straining your liver, it’s contraindicated.

For most of us most of the time you’re completely correct though.

In the case of these nasal spray decongestants I had a case of rebound congestion due to over-reliance on them while surviving some family bringing really bad colds into the house and my son starting daycare. It was really bad. I then managed by switching to an alternating schedule of pseudoephedrine and the nasal spray so I could reduce the physical dependency on the latter and get a good night’s sleep.

My doctor eventually cleared me to take an allergy spray medication (Fluticasone propionate) that is safer for long term use but generally not used for colds because it inhibits immune response and mask the symptoms which can cause new infections and hurt your ability to heal. Yet another case of the mundane medicine that is contraindicated. While seemingly being the wrong thing to be put on while fighting off infections it worked out great.

After four months I had seen enough child germs and no adult has brought their own plague or food poisoning (it was a very bad summer for me) and I finally became healthy again.