Patients Referred to the Chronic Pain Unit for Palliative Treatment With Ozone Therapy Between 2022 and 2025

Inclusion Criteria: 1. Adults \> = 18 years old. 2. Patients submitted to the Chronic Pain Unit of the Hospital Universitario de Gran Canaria Dr. Negrín for symptomatic/palliative treatment with ozone therapy because conventional treatment does not exist, it has been unsuccessful, or it is associated with high risk or high morbidity. 3. After evaluation of symptoms and patients, it exists a potential benefit of adding ozone treatment to the current treatment. 4. Patients have no contraindications for ozone treatment. 5. Patients have signed and dated the informed consent for the compassionated ozone treatment and the specific informed consent for this study Exclusion Criteria: 1. Age \< 18 years old. 2. Psychiatric illness or social situations that would limit compliance with study requirements. 3. Those who are incapable to fill in the scales used to measure variables. 4. Hemodynamically or clinically unstable patients or uncontrolled severe illness. 5. Uncontrolled cancer disease requiring chemotherapy treatment. 6. Life expectancy \< 6 months 7. Contraindication or disability or to attend scheduled treatments. 8. Known allergy to ozone. 9. Pregnancy at the time of enrollment (for systemic ozone therapy). 10 Hemochromatosis (for systemic ozone therapy). 11\. Known significant glucose-6-phosphate dehydrogenase deficiency (favism, acute hemolytic anemia) (for systemic ozone therapy). 12\. Patients who do not meet all the inclusion criteria