<unk>  sold under the brand name Entonox among others, is an inhaled gas used as a pain medication and together with other medications for anesthesia. Common uses include during childbirth, following trauma, and as part of end-of-life care. Onset of effect is typically within half a minute, and the effect lasts for about a minute. There are few side effects, other than vomiting, with short-term use. With long-term use anemia or numbness may occur. It should always be given with at least 21% oxygen. It is not recommended in people with a bowel obstruction or pneumothorax. Use in the early part of pregnancy is not recommended. Breastfeeding can occur following use.<unk> was discovered between 1772 and 1793 and used for anesthesia in 1844. It is on the World Health Organization's List of Essential Medicines. It often comes as a 50/50 mixture with oxygen. Devices with a demand valve are available for self-administration. The setup and maintenance is relatively expensive for developing countries.
Nitrous oxide 
Nitrosamine
Benzene
Nitrobenzene
Nicosan
Vinyl chloride
Carbon monoxide
Alkylphenol