Treatment adherence is defined by compliance with the dosage schedule (i.e., dose per dose and number of doses per day), as well as the duration of administration (i.e., number of days during which the dosage schedule must be followed).

Treatment adherence determines the therapeutic efficacy and the absence of toxicity of the prescribed medication. However, this adherence is far from being respected even by patients with serious pathologies such as patients living with HIV (PLWHIV). However, among PLWHIV, non-adherence is a significant source of virological failure and is difficult to assess because it is most often based on what the patient reports to their doctor. A currently used approach consists of determining the drug concentration in the blood and possibly that of its metabolite(s). However, determining a drug's blood concentration presents two major pitfalls: (i) it is necessary to take a blood sample, which remains an invasive procedure for the patient; (ii) for the vast majority of drugs, if the patient scrupulously adheres to the dosage schedule a few days before the blood sample is taken, the drug concentration is most often within the expected range. Therefore, a concentration in the reference range does not exclude partial or even total non-compliance between two medical visits. Saliva is a more easily accessible matrix than blood. However, the same representativeness problem is encountered due to the fact that saliva is in almost instantaneous equilibrium with blood.

Urine could be used to assess compliance. However, this requires multiple urine collections between two doses. This constraint is not compatible with the organization of clinical services. The objective is to determine intra-individual variability in the amount of antiretroviral (ARV) in different segments of the same strand of hair during periods of full treatment adherence.

This objective is preliminary to the use of hair as a tool for detecting treatment non-adherence in patients.

Two reference antiretroviral molecules will be documented: Emtricitabine and Lamivudine, as they are present, one or the other, in the majority of antiretroviral combination strategies.

Inclusion Criteria:

• Patient living with HIV
• Patient receiving stable antiretroviral therapy (i.e., no change in treatment strategy or dosage regimen) for at least 6 months.
• Patient receiving antiretroviral therapy based on emtricitabine or lamivudine.
• Patient identified as compliant based on patient follow-up data: (i) patient's reported adherence to the infectious disease physician (i.e., simple self-report), (ii) virological data (i.e., absence of blips in the last 18 months), (iii) pharmacological data (i.e., plasma antiretroviral concentrations within the expected range) if concentrations were previously measured as part of the patient's follow-up.
• Patient agreeing not to cut their hair to less than 6 cm of remaining length during the 6 months of the study.
• Patient agreeing to have their hair sampled at the end of the 6 months.
• Patients over 18 and under 70 years of age.
• Individuals who have not objected.
• Individuals enrolled in the French Health Insurance

Exclusion Criteria:

• Pregnant women.
• Patients planning to color/bleach their hair in the next 6 months.
• Patients planning to have their hair straightened/restyled in the next 6 months.
• Persons under judicial protection

patients with HIV and receiving antiretroviral therapy with Emtricitabine or Lamivudine.