Long-term (\>5 years), intermediate-term (1-5 years), and short-term low-dose naltrexone (LDN) users (\<12 months) will be contacted for a retrospective, observational assessment of their health status. Participants will be asked to complete a series of questionnaires assessing their quality of life, general physical and mental health, family history, the occurrence of age-related diseases, and immune status. Additionally, blood tests for immune and longevity markers will be optional for a subset of participants.
