Should I lower my spironolactone dose from 150mg to 100mg due to potassium level of 5.5?

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This is more complex than simply yes or no, and a full evaluation is really what's needed. Your age, current medications, diet and health influence this answer. But  one should certainly consider reducing this dose and speaking to your physician. Hyperkalemia (high potassium) is rare with spironolactone use in young women but this should be carefully followed 

If you have blood potassium level elevation while you are on this drug, go back to the doctor who is treating you, not doctors here on the internet