Protocol version 2.0: Removal of 12-week time limit for participants to be on stable background treatment, as the time needed to stabilise a participant on treatment can vary and should be the judgment of the principal investigator (treating physician) rather than within a prescribed time limit.

Protocol version 3.0 Update to events schedule: - Laboratory test will be performed at Visit 2 (baseline) as, given length of screening window, it is considered appropriate to have a baseline sample immediately prior to the commencement of dosing. - Participants should be observed for 1 hour after the first dose to monitor for any acute adverse effects of study drug administration (e.g., bronchospasm), per a comment from the Food and Drug Administration regarding potential for bronchospasm.

Protocol version 4.0: - Amendment to inclusion criteria 1, regarding the HRCT scan, to allow participants with a HRCT scan older than 12 months to undergo a HRCT scan and be considered for enrolment. - Dosing instructions changed from 2 inhalations with each capsule to 1 to 3 inhalations, to clarify that up to 3 inhalations may be required for proper dosing. HRCT=high resolution computerised tomography

Global Addendum 1 and 2, dated 22 April 2020 and 31 March 2021, respectively: Amended due to the global coronavirus disease pandemic and its potential impact on participant safety, eligibility and recruitment, as follows: - Use of telephone clinical assessments in lieu of on-site visits, where not safe or feasible - If not randomised within the 12-week screening window, the participant could return for a rescreen once safe. - Completion of home-based spirometry and HRQoL questionnaires/dyspnoea assessments via iPad or ‘interview mode’. - Pregnancy monitoring at home and communicated during telephone assessments. HRQoL=health-related quality of life

Protocol version 5.0: - Removal of stratified randomisation by SoC and increase in site number due to difficulties with enrolment in an acceptable timeframe, with no change in planned total number of participants. - Update to exclusion criteria to allow patients with squamous cell carcinoma to enrol, as no risk is foreseen. - Diffusion capacity for carbon monoxide and 6MWT added to withdrawal assessments as they are important assessments for IPF. - Addition and clarification of rescreen procedures to be performed which included DLCO and spirometry. SoC=standard of care; 6MWT=6-minute walk test; IPF=idiopathic pulmonary fibrosis; DLCO=diffusion capacity for carbon monoxide;

Protocol version 6.0: - Following the DSMB’s recommendation, participants on SoC/approved treatment for IPF were excluded, and the GB0139 10 mg treatment arm was removed. Eligible participants were to be randomised in a 2:1 ratio to 1 of the 2 treatment arms, 3 mg and placebo, to maintain the chance (2/3) of receiving an active treatment at randomisation for individual participants, compared with the previous design - The primary objective was updated to reflect to the current study design - Key secondary endpoints were updated to include: - Change from baseline in SGRQ total score at Week 52 - Moved time to first hospitalisation, respiratory related to the key secondary endpoints - Exploratory endpoints were updated to include: - Time to initiation of pirfenidone or nintedanib treatment for SoC2 participants up to the time when SoC1 and SoC2 were removed - Time to termination of pirfenidone or nintedanib treatment for SoC1 participants up to the time when SoC1 and SoC2 were removed - Screening period duration was updated to 6 weeks - Change of follow-up to be conducted by phone call from 1 week and up to 2 weeks after the last study visit - Exclusion criteria were updated to exclude participants from the trial that: - Currently receiving nintedanib and pirfenidone - Previously using GB0139 or were randomised in GALACTIC-1 - Previously used nintedanib or pirfenidone within 7 days of initiation of screening - Previously used investigational drugs within 30 days of initiation of screening - Participate in another clinical trial - Have hypersensitivity to the active substance (GB0139) or the excipient (lactose) - Duration of IPF diagnosis to screening was changed from 3 to 5 years to facilitate enrolment under the updated patient selection criteria - Coronavirus disease vaccines were added under permitted medications No participants in Belgium enrolled in new trial design DSMB=Drug Safety Monitoring Board;SGRQ=St. George’s Respiratory Questionnaire

Protocol version 7.0: - Exclusion criterion number 11 was updated to exclude only participants participating in another interventional clinical trial, based on the study investigator’s suggestion. - Correction of secondary endpoint – proportion of participants with an absolute decline from baseline in FVC% pred of ≤10% and ≤5 at Week 52 (from >10% and >5%, respectively). The revised wording is a definition of a responder, rather than a progressor. - Sample size justification updated. The level of significance and power of the study were revised to be more reflective of a Phase 2 study. As a result of increasing the significance level to 10% and reducing the power to 75%, the sample size decreased to 141 participants. The level of confidence was changed from 95% to 90% to reflect the new level of significance. - Time to termination of pirfenidone or nintedanib treatment was removed from exploratory endpoints as the use of these drugs had been systematically curtailed, so was no longer relevant. FVC=forced vital capacity