Chronic pain is often associated with a chronic stress and HHSG axis plays a pivotal role in maintaining homeostasis. The literature reports that pain in patients treated with opioids, significant changes are taking place in this axis with a collapse in hormone concentrations that are correlated with the decline on tests of quality of life and psychological testing. The investigators hypothesis is that this "endocrinopathy" could also be present in patients treated for neuropathic pain with other drug classes as opiates (antidepressants, antiepileptics), and may explain, at least in part, the impairement of the quality of life of these patients.

Day of inclusion: Blood sample for analysis of several hormones (cortisol, ACTH, SHBG, total testostérone et S-DHEA, βœstradiol et progestérone for women, LH, FSH).

Day +1: salivary samples (at wake-up, 30 minutes after wake-up, at lunch, at 06:00 pm and before sleep).

Day +2: salivary samples (at wake-up, 30 minutes after wake-up).

Inclusion Criteria:

• Group of patients
• Patients older than 18 years,
• Male or Female with BMI between 18 and 35,
• Patients with chronic neuropathic pain for more than six months, except to diabetes or central neuropathic pain
• Patients receiving systemic therapy for treating chronic neuropathic pain such as antidepressants, anticonvulsants or opiates for at least 6 months.

Group of healthy volunteers

• non-painful healthy volunteers matched by age, sex, BMI and menopausal status for women,
• Free of analgesics within 8 days before the test,
• Aged over 18 years,
• Male or Female,

Exclusion Criteria:

• Subjects with a medical history and / or surgical judged by the investigator or his representative as being incompatible with the test
• Patients treated only by topical treatment (lidocaine patch only for example)
• Pateints receiving corticosteroid treatment at the time of enrollment, or who received such treatment during the last 6 months (regardless of the dosage form and dosage),
• Inflammatory and evolutive pathology requiring long term treatment,
• Type 2 diabetes,
• Postmenopausal women with replacement therapy,
• Weight change of more than 5% within 3 months before the study,
• BMI <18 or> 35,

Patients older than 18 years,

• Male or Female with BMI between 18 and 35,
• Patients with chronic neuropathic pain for more than six months, except to diabetes or central neuropathic pain
• Patients receiving systemic therapy for treating chronic neuropathic pain such as antidepressants, anticonvulsants or opiates for at least 6 months.

Group of healthy volunteers

• non-painful healthy volunteers matched by age, sex, BMI and menopausal status for women,
• Free of analgesics within 8 days before the test,
• Aged over 18 years,
• Male or Female,