Inclusion Criteria:  Male or female aged 18 to 55 years inclusive BMI ranging from 18 to 32 kg/m2, inclusive Adequate venous access Healthy subjects and non-dependent who are non dependent opioid experienced users, opioid experience defined as exposure to an opioid on at least 1 occasion prior to screening  Exclusion Criteria:  History of clinically significant disease Significant trauma injury, major surgery, open biopsy within 30 days prior to screening Subject who has a difficult airway for intubation. Following an abnormal diet 4 weeks prior to screening Use of over-the-counter medications, dietary supplements, herbal products, vitamins or opioid analgesics 14 days before intervention Use of enzyme altering drugs 30 days before intervention Use of nasal products 28 days before intervention and throughout the study Previous or current opioid, alcohol, or other drug dependence Donated or received blood 30 days before intervention Women who are pregnant or breastfeeding at screening Women of childbearing potential unless surgically sterile or use effective contraception Current or recent upper respiratory tract infection Allergic to nalmefene or naloxone or known hypersensitivity reaction to plastics.