Re: citalopram and clarythromycin
Both drugs can prolong the QT interval, which is probably where you're getting these scare stories from.
This would be concerning in an old, "failing health" individual, but in a young, healthy person, this wouldn't be as much of a concern, especially with a low or moderate dose. This is very much so a clinical decision, with risk:benefits being established.
As I don't know anything about you at all, I am only giving very basic advice, not specific to your case.
You should follow your pharmacists advice.
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Healthcare Professional with Health Anxiety
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