My Bp Had Never Been High. However During A Recent

My bp had never been high. However during a recent doctor visit it was 133/99 and so my primary doc decided to put me on losartan/hctz 50mg/12mg. I am only taking half of the dosage because I've read that losartan is given to patients with heart failure of which I have never had. Ian scared to take full dosage. This morning was when I started taking this medicine. I took half a pill for the very first time and it shot my blood pressure up to 156/101. I thought meds were suppose to keep bp down. Why did my bp go up after taking this medication for the very first time?