This observational study aims to examine the relationship between opioid use and redox balance in adults. Redox balance reflects the level of oxidative stress in the body, which is known to play an important role in many biological processes and diseases.

Participants who use opioids will be included in the study. No experimental treatment or changes to current medical care will be provided as part of this study. Biological samples may be collected to assess redox-related biomarkers, and relevant clinical and demographic information will be recorded.

The results of this study are expected to improve understanding of how opioid exposure is associated with redox balance in adults. This information may help inform future research on the biological effects of opioids and potential strategies to reduce harm associated with long-term opioid use.

Opioids are widely used for the management of acute and chronic pain; however, prolonged opioid exposure has been associated with a range of systemic effects beyond analgesia. Increasing evidence suggests that oxidative stress and alterations in redox balance may play a role in the biological effects of opioids, potentially contributing to tissue damage, inflammation, and other adverse outcomes.

The OpioidRedoxStudy II is an observational study designed to further investigate the association between opioid use and redox balance in adults. This study builds on previous findings by focusing on redox-related biomarkers that reflect oxidative and antioxidative processes in the human body. The study does not involve any experimental intervention, randomization, or modification of participants' current medical treatment.

Participants using opioids will be assessed using biological samples collected according to the study protocol. These samples will be analyzed for markers related to redox balance. In addition, relevant clinical, demographic, and opioid exposure data will be collected to allow for exploratory analyses of associations between opioid use patterns and redox-related measures.

The primary objective of this study is to characterize the relationship between opioid exposure and redox balance in adults. Secondary objectives include exploring potential associations between redox-related biomarkers and clinical characteristics. The findings of this study are intended to contribute to a better understanding of the biological effects of opioid use and to support future research aimed at reducing opioid-related harm.

Inclusion Criteria:

• Adults aged 18 years or older
• Receiving opioid therapy (tramadol, tapentadol, morphine, fentanyl, or buprenorphine) as part of routine clinical care
• Stable opioid treatment for at least a predefined minimum period prior to enrollment (according to the study protocol)
• Ability to provide written informed consent
• Ability to comply with study procedures, including blood sampling and completion of questionnaires

Exclusion Criteria:

• Acute opioid intoxication or withdrawal at the time of enrollment
• Use of investigational drugs or participation in another interventional clinical trial that could interfere with study outcomes
• Severe acute illness or unstable medical condition that, in the investigator's judgment, would interfere with study participation
• Known pregnancy or breastfeeding
• Inability to provide informed consent
• Any condition that, in the opinion of the investigator, would make participation unsafe or compromise the quality of the collected data

The study population consists of adult patients receiving opioid therapy as part of routine clinical care. Participants are treated with tramadol, tapentadol, morphine, fentanyl, or buprenorphine and are enrolled into predefined observational cohorts based on the type of opioid used. The study population includes individuals with ongoing opioid exposure who are able to provide informed consent and comply with study procedures.

Individual participant data will not be shared due to the sensitive nature of the collected data, including genetic information and detailed clinical variables. Data sharing is further restricted to ensure participant confidentiality and compliance with applicable data protection regulations.