A Study to Test Tetrandrine Tablets for Connective Tissue Disease-Related Lung Disease

Inclusion Criteria: * Patients who voluntarily participate and sign the informed consent form * Male or female patients aged 18-80 years (inclusive) * Patients meeting the diagnostic criteria for connective tissue disease-related interstitial lung disease per the 2018 Chinese Expert Consensus at screening * FVC ≥40% of predicted value at screening * Fertile male or female patients must agree to use effective contraception from signing informed consent until 3 months after the last study drug dose (Exemptions: postmenopausal women \>50 years with amenorrhea for \>1 year, or surgically sterilized women) * Patients on stable doses of prednisone (≤20 mg/day or equivalent) or immunosuppressants for at least 4 weeks prior to study entry, with dose adjustments not exceeding this during the double-blind period Exclusion Criteria: * Treatment with tetrandrine or other antifibrotic drugs within 1 month before screening * Diabetes with fasting blood glucose greater than 11.1 mmol per L * Resting arterial oxygen partial pressure less than 50 mmHg * Active peptic ulcers or bleeding disorders * Tumors with expected survival less than 1 year * Active pulmonary tuberculosis * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) 5 times the upper limit of normal (ULN) or higher, or ALT or AST 3 times ULN or higher with total bilirubin 2 times ULN or higher * Creatinine clearance less than 30 mL per min (per Cockcroft-Gault formula) or patients receiving dialysis * Known allergy to tetrandrine or its excipients * Severe psychological, mental, cognitive, or intellectual impairments that may affect compliance * Pregnant or breastfeeding women, or those planning pregnancy within 3 months after the last study drug dose * Participation in another clinical trial within 3 months before screening * Patients deemed unsuitable for the study by the investigator * Clinically significant environmental exposure history that may cause pulmonary fibrosis (e.g., amiodarone, asbestos, beryllium, radiation)