Study plan: Briefly, 36 patients with CF, > 12 years of age, who are homozygous for F508del and have been on treatment with Orkambi™ for at least 3 months will be recruited for this trial. This trial will be randomized 1:1 with placebo (n=18 for each group). After signing informed consent at the screening visit, subjects will perform spirometry, determine sweat chloride, take blood, and test for pregnancy where applicable. Eligible patients will complete visits as outlined below. Quality of life will be assessed by CF quality of life questionnaire - revised (CFQ-R), 12). NPD will use standard protocols and so will nasal cell harvest (see below for assessments). Cytokines will be measured from nasal fluid recovered by Leukosorb filter paper (13). There will be two visits for these different nasal assessments to assure that nasal cell fluid and cell collection will not influence NPD and vice versa. After assessing baselines, a daily dose of 50 mg losartan or placebo will be started. A safety visit will occur after 7 days of treatment (± 2 days) and the losartan dose (or placebo) increased to 100 mg daily (higher dose is likely needed to get anti-inflammatory effect in airways if present). Since this trial assesses anti-inflammatory effects of losartan (and lack of placebo), the total duration will be 14 weeks to achieve 12 weeks of treatment with the higher dose of losartan (or placebo).