Concentrations of Nitrous Oxide in Blood, Exhaled Air and Urine After Various Types of Exposure.

For arm 1, 2, and 3: Inclusion Criteria: * Age 18-65 years * Able to understand Danish * Willing to use effective contraception for 24 hours after the end of exposure (oral contraceptives, contraceptive implant, transdermal patch, vaginal ring, or injectable contraceptives) * Written informed consent Exclusion Criteria: * Current or past abuse of drugs, nitrous oxide (N₂O), or alcohol * A psychiatric disorder requiring medical treatment, including severe depression * A diagnosis of epilepsy * Symptoms of peripheral neuropathy * Significant cardiac or pulmonary disease * Previous allergic or adverse reaction to N₂O * Diving within the past 2 days * Inability to refrain from diving for 2 days after the study * Occupational exposure to N₂O * Use of N₂O within the past 3 months * Treatment with methotrexate, benzodiazepines, opioids, or other centrally depressant drugs * Recent intraocular gas injection * Known impaired liver or kidney function * Pregnant or breastfeeding women (fertile women, defined as amenorrhea for less than 12 months, must have a negative hCG pregnancy test prior to receiving the study intervention)