The purpose of this study is to assess the efficacy and safety of sublingual naloxone in the treatment of chronic itch in patients under arsenic exposure.

This study aims to determine the efficacy and safety of sublingual naloxone in the treatment of chronic, refractory itch in patients under long-term arsenic exposure. In this study, 120 subjects with a moderate-to-severe symptom of itching (numeric rating scale, NRS≥3) will be recruited and randomly treated with either sublingual naloxone (60 subjects) or placebo (60 subjects). The severity of itching will be evaluated in the wash out phase, baseline, and one week after the treatment through reporting of subjective symptomatology (itch NRS) via the interview. Quality of sleep measured by the Pittsburgh Sleep Quality Index (PSQI) and Dermatology Life Quality Index (DLQI) will serve as the secondary outcome.

Inclusion Criteria:

1. Aged 18 years or over and without diseases except arsenic-related pruritus
2. Ability to study protocol and to give informed consent by himself/herself voluntarily
3. The number of male or female subjects is required more than 1/3 of the total number of subjects
4. Numeric Rating Sscale≥3 at the baseline
5. Subjects taking hormone-containing medications must be on a stable dose for 6 months prior to study start to avoid any confounding influence on sensory and pain perception

Exclusion Criteria:

1. Use of oral anti-inflammatory medications for 2 weeks prior to the study start.
2. Use of oral anti-histamines for 2 weeks prior to the study start.
3. Use of topical or oral anti-pruritic agents for 2 weeks prior to the study start.
4. Use of oral neuromodulatory agents for 2 months prior to study start.
5. Current use of chronic pain medications (including opioids, antidepressants and anti-epileptic drugs).
6. Use of nicotine-containing products for the past 6 months prior to study start.
7. History of basic itchy dermatological diseases before such as eczema wich may influence the judgement of drug efficacy.
8. Unstable thyroid function within the past 6 months prior to study start to exclude thyroid-related neuropathy.
9. Known history of central or peripheral nervous system dysfunction.
10. History of acute hepatitis, chronic liver disease or end stage liver disease.
11. History of human immunodeficiency virus (HIV) or acquired immune deficiency syndrome.
12. History of neuropathy associated with chronic obstructive pulmonary disease, diabetes mellitus, documented exposure to organophosphates or heavy metals or polychlorinated biphenyls.
13. Known nutritional deficiency (vitamin B12, vitamin D, iron or zinc) within 3 months prior to the study start.
14. Use of illicit drugs within the past 6 months prior to study start.
15. Lyme disease, porphyria, rheumatoid arthritis, Hansen's disease (leprosy) or use of antineoplastic chemotherapeutic agents.
16. Patients considered by researchers that are not suitable to the study.

Study Protocol; Statistical Analysis Plan (SAP); Informed Consent Form (ICF) can be shared for the purpose of academic communication

Since the official start of the trial to the end of the trial

Describe clearly about the reason of review

2 weeks

The participants will not be informed whether the drug they received is naloxone or placebo. The investigators will remove the package of the drugs and use the unified package for both of the drugs.