they just felt better and convinced themselves they don't need it
This one isn't a third world problem. I've encountered this one a few times and I don't even work anywhere near health. I think it still frustrates me on a level but if I were to encounter this kind of situation again (the last time was when I was at uni) I think with very few exceptions I would just be openly exasperated.
Some part of the problem includes not really having that highest level of insight and acceptance of things the way they are much like how diabetics or hypertensives still don't avoid eating foods that make their conditions worse because they "feel better" or their meds are working for them enough to not worry. Dosages will depend on the person's lifestyle like what if they became fat for a few months that now the amount they're getting is less than their body weight as prescribed or when they are in a more stressful environment that may require increasing their usual dose.