So far it has lasted 9 weeks. I was on amlodipine for high blood pressure for several years. Then my consultant ordered me to double the dose "and go for perfection". Before the week was out, I had developed an all-over skin rash. So I stopped taking the drug. Antihistamine tablets ease the itching a little, but after more than 2 months the spots are still angry and spreading. How long does it last?