Inclusion Criteria:  1. Written informed consent consistent with GCP and local laws signed prior to entry into the study.  2. Patients with LAM and > 18 years-old with:  FEV1 > 35% and DLCO > 20% Oxygen saturation (SpO2) > 85% by pulse oximetry while breathing ambient air at rest Patients with a definite diagnosis consistent with LAM prior to screening based on International consensus criteria within 10 years prior to randomization HRCT within 12 months prior to randomization with central reading demonstrating a radiological pattern suggesting LAM and some other criteria for initiating sirolimus (symptoms, FEV1 decline or the presence of abdominal lynphangioleiomiomas).  Exclusion Criteria:  Concomitant use of other HR1 antagonist Hypersensitivity to HR1 antagonists Current smoker or ex-smoker having quit smoking < 4 months prior to firs screening visit - Use of systemic immunosuppressants or chemotherapy within 30 days of screening. Receiving oral corticosteroids>15mg/day, vasodilator therapies for pulmonary hypertension (e.g., bosentan), unapproved and/or investigational therapies for LAM or administration of such therapies within 4 weeks of initial screening. At baseline/screening visit, values of liver transaminases above 3 times upper limit, alkaline phosphatase above 2.5 times upper limit, or bilirubin above 1.5 times upper limit Creatinine clearance (CrCl)<60ml/min (determined by Cockcroft-Gault Equation) at baseline/ screening visit. Patients treated with strong inhibitors and inducers of CYP either during the study or 14 days prior to enrolment in the study: antifungals (e.g., ketoconazole, itraconazole), clarithromycin, telithromycin, cobicistat, protease inhibitors (e.g., atazanavir, ritonavir, and saquinavir) and grapefruit juice, phenytoin, carbamazepine, barbiturates, rifampin. Current allergic asthma or other major allergic diseases that requires different daily anti- histaminic treatment. History of coexistent and clinically significant (in the opinion of the Investigator) chronic obstructive pulmonary disease (COPD), bronchiectasis, asthma, inadequately treated sleep- disordered breathing, or any clinically significant pulmonary diseases other than LAM.