Inclusion Criteria:

1. Male or female, aged greater than or equal to 40 years.
2. A diagnosis of Idiopathic Pulmonary Fibrosis (IPF) based on local or regional multi-disciplinary consensus according to the latest international guidelines (50).
3. Patients may be receiving licensed anti-fibrotic medication (for at least 4 weeks prior to randomisation with no planned amendments for at least 4 weeks post-randomisation).
4. Able to provide informed consent.

Additional Inclusion Criteria for cough count sub-study:

1. Pre-existing diagnosis of persistent cough (defined as troublesome for more than 8 weeks prior to study enrolment).

Exclusion Criteria:

1. Patients unable to comply with study assessments including the ability to complete reliable spirometry assessments.
2. Concomitant use of a proton pump inhibitor (PPI) or prokinetic drugs (cisapride, domperidone, metoclopramide, erythromycin, prucalopride etc.) within 2 weeks prior to randomisation.
3. Patients with a self-reported respiratory tract infection within 4 weeks of screening (defined as two or more of: increased cough, sputum or breathlessness and requiring antimicrobial therapy).
4. Significant co-existing respiratory disease (defined as a respiratory condition that exhibits a clinically relevant effect on respiratory symptoms and disease progression as determined by the PI). The presence of traction bronchiectasis is permitted.
5. Patients with an FEV1/FVC<0.7.
6. Significant medical, surgical or psychiatric disease that in the opinion of the patient's attending physician would affect subject safety or influence the study outcomes including liver failure (e.g. serum transaminase > 2 x upper limit of normal (ULN), Bilirubin > 1.5 x ULN (unless the patient has Gilbert's Syndrome) and chronic kidney disease (CKD) greater than stage 3 , erosive oesophagitis, Barrett's oesophagus or any condition requiring lifelong proton pump inhibitor use.
7. Known allergy to proton pump inhibitors or the contents of placebo.
8. Concomitant use of atazanavir, ketoconazole, itraconazole, tacrolimus, methotrexate, fluvoxamine (see section 6.4.5).
9. Females who are of childbearing potential or lactating. A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. A high FSH level in the postmenopausal range may be used to confirm a post-menopausal state in women not using hormonal contraception or hormonal replacement therapy. However in the absence of 12 months of amenorrhea, a single FSH measurement is insufficient.
10. Receipt of another investigational drug or biological agent associated with another clinical trial within the 4 weeks prior to TIPAL study enrolment or 5 times the drug half-life, whichever is the longer.
11. Receiving long-term oxygen therapy.
12. Patients with hypomagnesemia (defined as magnesium ≤0.6 mmol/L).