Can morphine or pregabalin finally stop that nagging cough?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Adults (≥18 years old) with either: 2. Refractory chronic cough (RCC), defined as having one or more identifiable causes of cough (asthma, allergic rhinitis, and/or GERD), but with previous trials of treatment targeting the underlying condition leading to no cough resolution; OR 3. Unexplained chronic cough (UCC), defined as having a cough lasting \>8 weeks with (i) a normal chest X-ray/CT in the last 5 years and since the onset of chronic cough; (ii) FEV1 and FVC ≥80% predicted or \>lower limit of normal (LLN); (iii) FEV1/FVC ≥0.7 or \>LLN; (iv) no evidence of asthma; and (vi) no regular symptoms of nasal/reflux disease. Exclusion Criteria: 1. Those who, in the opinion of the investigator, have previously tried low-dose morphine, pregabalin, and/or CCT with full intervention fidelity for the treatment of RCC/UCC; 2. Are currently taking morphine or pregabalin for the treatment of any indication (i.e., RCC/UCC or chronic pain);\* 3. Are currently taking other centrally-acting medication (i.e., gabapentin, amitriptyline, dextromethorphan) for the treatment of any indication (i.e., RCC/UCC, seizures, or depression);\* 4. Have a history of opioid or substance abuse that, in the opinion of the investigator, may interfere with the conduct of the study; 5. Are a current smoker, or ex-smoker with a \>20 pack-year history who have abstained from smoking for \<6 months; 6. Have cough due to angiotensin-converting enzyme inhibitor use; 7. Have symptoms of an upper respiratory infection within the last month that have not resolved; 8. Had an asthma exacerbation within the last month that requires an increase or start of an oral corticosteroid; 9. Have other primary pulmonary disorders, including pulmonary embolism, pulmonary hypertension, lung cancer, cystic fibrosis, radiologically-proven emphysema, interstitial lung disease, or severe bronchiectasis; 10. Have language, memory, cognitive, or psychiatric issues that may prevent optimal participation; 11. Have creatinine clearance \<15 mL/min, including individuals with end-stage renal disease who require hemodialysis or peritoneal dialysis; 12. Have any other condition that, in the opinion of the qualified investigator, may adversely affect the participant's ability to complete the study or its measures or pose significant risk to the participant; 13. Have participated in another clinical trial of an investigational medicinal product within 30 days; 14. Pregnant or breastfeeding; or 15. Females of child-bearing potential who: 1. Do not agree to use a medically approved method of birth control for the duration of the study. All hormonal birth control must have been in use for a minimum of 3 months. 2. Acceptable methods of birth control include oral contraceptives, hormone birth control patch, vaginal contraceptive ring, injectable contraceptives, or hormone implant, double-barrier method, intrauterine devices, non-heterosexual lifestyle or agrees to use contraception if planning on changing to heterosexual partner(s), vasectomy of partner at least 6 months prior to screening. 3. Females who are not of child-bearing potential will be defined as females who have undergone a sterilization procedure (e.g., hysterectomy, bilateral oophorectomy, bilateral tubal ligation, complete endometrial ablation) or have been post-menopausal for at least 1 year prior to screening. * Participants taking any of the above medications at baseline will only be eligible if they are willing and medically able to safely discontinue them at least 2 weeks prior to the first study visit. Eligibility will be confirmed by the local study investigator prior to enrolment.