asphyxiant

https://doi.org/10.1351/goldbook.15483
Substance that blocks the transport or use of oxygen by living organisms.
Example: Included are both physical (nitrogen gas) and chemical (carbon monoxide) asphyxiants.
Source:
PAC, 2007, 79, 1153. (Glossary of terms used in toxicology, 2nd edition (IUPAC Recommendations 2007)) on page 1171 [Terms] [Paper]