Hi Welcome to HCM. I appreciate your concern for the safety of Losartan and the uncontrolled BP. Losartan is known to cause the following side effects: Dry cough, swelling of the face (eyes or lips due to allergy), increase in blood potassium level. The possible reason behind persistent high BP despite of taking Losartan could be inadequate dose for that you may need another drug like Hydrochlorthiazide to be combined along with Losartan. Other possibilities include concomitant use of NSAID pain killers, lack of physical activity, cigarette smoking (if you smoke), increased intake of dietary salt and red meat, etc. You are hereby advised to visit your treating doctor for further evaluation and use of combined medications with lifestyle modifications to control your BP. Hope this answers your query. Rate this answer, if you are convinced.