BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a progressive disease that leads to lung scarring. Cough is reported by 85% of patients with IPF and can be a distressing symptom with a significant impact on patients' quality of life. There are no proven effective therapies for IPF-related cough. Whilst morphine is frequently used as a palliative agent for breathlessness in IPF, its effects on cough have never been tested. PAciFy Cough is a multicenter, double-blind, placebo-controlled, crossover trial of morphine sulphate for the treatment of cough in IPF. METHODS: We will recruit 44 subjects with IPF prospectively from three interstitial lung disease units in the UK, namely the Royal Brompton Hospital, Manchester University NHS Foundation Trust (MFT) and Aintree University Hospital NHS Foundation Trust. Patients will be randomised (1:1) to either placebo twice daily or morphine sulphate 5 mg twice daily for 14 days. They will then crossover after a 7-day washout period. The primary endpoint is the percent change in daytime cough frequency (coughs per hour) from baseline as assessed by objective cough monitoring at day 14 of treatment. DISCUSSION: This multicentre, randomised trial will assess the effect of opioids on cough counts and cough associated quality of life in IPF subjects. If proven to be an effective intervention, it represents a readily available treatment for patients. TRIAL REGISTRATION: The study was approved by the UK Medicines and Healthcare Regulatory Agency (Ref: CTA 21268/0224/001-0001 - EUDRACT 2019-003571-19 - Protocol Number RBH2019/001) on 08 April 2020, in compliance with the European Clinical Trials Directive and the Medicines for Human Use (Clinical Trials) Regulations 2004 and its subsequent amendments. The study was provided with ethical approval by the London Brent Research Ethics Committee (Ref: 20/LO/0368) on 21 May 2020 and is registered with clinicaltrials.gov (NCT04429516) on 12 June 2020, available at https://clinicaltrials.gov/ct2/show/NCT04429516.