I don't think that the medication becomes less effective, it's your blood pressure problem (for me, it's hereditary) that deteriorates as you get older. After various medications off/on over the years it seemed like mine had stabilised last summer, but it went up again with a vengeance a few months later. At the moment I'm on two medications, one in the morning and one in the evening (which helps me to feel less dizzy and unwell). I'm back with the blood pressure nurse on Monday and hoping I'm stable again, so that I don't have to keep measuring twice a day and so that I can go ahead with surgery!