Inclusion Criteria:

• Able and willing to comply with the protocol requirements and signed the informed consent form (ICF) as approved by the Independent Ethics Committee (IEC)/Institutional Review Board (IRB), prior to any screening evaluations.
• Subject must be able and willing to comply with restrictions on prior and concomitant medication.
• Male or female subject aged ≥40 years on the day of signing the ICF.
• A diagnosis of IPF within 5 years prior to the screening visit, as per applicable ATS/ERS/JRS/ALAT guideline at the time of diagnosis.
• Chest HRCT historically performed within 12 months prior to the screening visit and according to the minimum requirements for IPF diagnosis by central review based on subject’s HRCT only (if no LB available), or based on both HRCT and LB (with application of the different criteria in either situation). If an evaluable HRCT <12 months prior to screening is not available, an HRCT can be performed at screening to determine eligibility, according to the same requirements as the historical HRCT.
• Subjects receiving local standard of care for the treatment of IPF, defined as either pirfenidone or nintedanib at a stable dose for at least two months before screening, and during screening; or neither pirfenidone or nintedanib (for any reason). A stable dose is defined as the highest dose tolerated by the subject during those two months.
• The extent of fibrotic changes is greater than the extent of emphysema on the most recent HRCT scan (investigator-determined).
• Meeting all of the following criteria during the screening period:
  • FVC ≥ 45% predicted of normal;
  • Forced expiratory volume in 1 second (FEV1)/FVC ≥ 0.7;
  • DLCO corrected for Hb ≥ 30% predicted of normal.
• In a stable condition and suitable for study participation based on the results of a medical history, physical examination, vital signs, 12-lead ECG, and laboratory evaluation. Stable condition is based on the clinical judgment of the investigator; co-morbidities should be treated according to the local applicable guidelines.  Concomitant medication for chronic co-morbidities should have been stable from 4 weeks prior to screening and during the screening period (stable defined as no clinically relevant change according to the investigator’s judgment).
• Estimated minimum life expectancy of at least 30 months for non-IPF related disease in the opinion of the investigator.
• Male subjects and female subjects of childbearing potential agree to use highly effective contraception/preventive exposure measures from the time of first dose of IMP (for the male subject) or the signing of the ICF (for the female subject), during the study, and until 90 days (male) or 30 days (female) after the last dose of IMP.
• Able to walk at least 150 meters during the 6MWT at screening Visit 1; without having a contraindication to perform the 6MWT or without a condition putting the subject at risk of falling during the test (investigator’s discretion). The use of a cane is allowed, the use of a stroller is not allowed at all for any condition. At Visit 2, for the oxygen titration test, resting SpO2 should be ≥88% with maximum 6 L O2/minute; during the walk, SpO2 should be ≥ 83% with 6 L O2/minute or ≥ 88% with 0, 2 or 4 L O2/minute.
• Able to read and complete the EQ-5D, SGRQ, LCQ, K-BILD questionnaire, and VAS by themselves.
• Able to understand the importance of adherence, and willing to comply to study treatment, study procedures and requirements as per study protocol, including the concomitant medication restrictions.

Exclusion Criteria: 

• Investigator or other study staff or relative thereof who is directly involved in the conduct of the study.
• Any clinical condition or other condition or circumstance that, in the opinion of the investigator, may make a subject unsuitable for inclusion or unlikely or unable to complete the study or comply with study procedures and requirements.
• Previous participation in a clinical study with GLPG1690 (active or placebo).
• Known hypersensitivity to any of the IMP ingredients or a history of a significant allergic reaction to any drug as determined by the investigator (e.g., anaphylaxis requiring hospitalization).
• A current immunosuppressive condition (e.g. human immunodeficiency virus [HIV] infection, congenital, acquired, medication-induced).
• Positive blood testing for hepatitis B surface antigen (HBS Ag) or hepatitis C virus (antibody, confirmed by hepatitis C virus (HCV) RNA positivity).
  • Note: Subjects with a resolved hepatitis A at least 3 months prior to screening can be screened.
• History of malignancy within the past 5 years (except for carcinoma in situ of the uterine cervix, basal cell carcinoma of the skin that has been treated with no evidence of recurrence, prostate cancer that has been medically managed through active surveillance or watchful waiting, squamous cell carcinoma of the skin if fully resected, and Ductal Carcinoma In Situ).
• Clinically significant abnormalities detected on ECG of either rhythm or conduction, a QTcF > 450 ms, or a known long QT syndrome.
• Currently taking medication known to be a substrate mainly metabolized by CYP2C8.
• Currently taking medication known to be strong inducers of CYP3A4, and also including St-John’s Wort.
• Currently taking medication known to be strong inhibitors of CYP3A4.
• Currently taking medication known to be potent inducers of P-gp.
• Currently taking medication known to be potent inhibitors of P-gp.
• Acute IPF exacerbation within 6 months prior to screening and/or during the screening period. The definition of an acute IPF exacerbation is as follows:
  • Previous or concurrent diagnosis of IPF; Acute worsening or development of dyspnea typically < 1 month duration; Computed tomography with new bilateral ground-glass opacity and/or consolidation superimposed on a background pattern consistent with usual interstitial pneumonia pattern and deterioration not fully explained by cardiac failure or fluid overload.
• Lower respiratory tract infection requiring antibiotics within 4 weeks prior to screening and/or during the screening period.
• Interstitial lung disease associated with known primary diseases (e.g. sarcoidosis and amyloidosis), exposures (e.g., radiation, silica, asbestos, and coal dust), or drugs (e.g., amiodarone).
• History of lung volume reduction surgery or lung transplant.
  • Note: being on a transplant list is allowed.
• Diagnosis of severe pulmonary hypertension (investigator-determined).
• Unstable cardiovascular, pulmonary (other than IPF), or other disease within 6 months prior to screening or during the screening period (e.g., acute coronary disease, heart failure, and stroke).
• Had gastric perforation within 3 months prior to screening or during screening, and/or underwent major surgery within 3 months prior to screening, during screening or have major surgery planned during the study period.
• A history of being admitted to an institution under an administrative or court order, if applicable by local legislation, as well as any subjects falling into any of the categories of persons listed by applicable law and regulations as protected persons for which participation in a study is prohibited or subject to restrictions.
• Moderate to severe hepatic impairment (Child-Pugh B or C) and/or Abnormal LFT at screening, defined as AST, and/or ALT, and/or total bilirubin ≥ 1.5xULN, and/or GGT ≥ 3xULN. Retesting is allowed once for abnormal LFT.
• Abnormal renal function defined as estimated creatinine clearance, calculated according to Cockcroft-Gault calculation (CCr) < 30 mL/min. Retesting is allowed once. Hb level < 10 g/dL. Retesting is allowed once.
• Participation in a drug, device, or biological investigational research study, concurrently with the current study, or within 5 half-lives of the agent (or within 8 weeks when half-life is unknown) prior to screening, or prior participation in an investigational drug antibody study within 6 months prior to screening.
• Use of any of the following therapies within 4 weeks prior to screening and during the screening period, or planned during the study: warfarin, imatinib, ambrisentan,azathioprine, cyclophosphamide, cyclosporine A, bosentan, methotrexate, sildenafil (except for occasional use), prednisone at steady dose >10 mg/day or equivalent.
• Current alcohol or substance abuse in the opinion of the investigator.
• Pregnant, breastfeeding, or planning to become pregnant or breastfeed during the study treatment or within 30 days after the last dose of IMP.