Methemoglobin: NO is absorbed into the blood where its binds to the ion of the heme protein, subsequently producing nitrosyl-hemoglobin, which is oxidized to methemoglobin with the release of nitrates  . Methemoglobin levels should be measured frequently and kept <%. With standard iNO doses, methemoglobinemia is unusual. In the Neonatal Inhaled Nitric Oxide Study Group (NiNOS) trial, the peak level of methemoglobin was %±%  . Premature infants are at a higher risk of methemoglobin toxicity due to reduced levels of methemoglobin reductase, but at iNO doses of <20 ppm, methemoglobin levels were not elevated   .
Regardless of which inhalant is used, inhaling vapours or gases can lead to injury or death. One major risk is hypoxia (lack of oxygen), which can occur due to inhaling fumes from a plastic bag, or from using proper inhalation mask equipment (., a medical mask for nitrous oxide) but not adding oxygen or room air. Another danger is freezing the throat. When a gas that was stored under high pressure is released, it cools abruptly and can cause frostbite if it is inhaled directly from the container. This can occur, for example, with inhaling nitrous oxide. When nitrous oxide is used as an automotive power adder , its cooling effect is used to make the fuel-air charge denser. In a person, this effect is potentially lethal). Many inhalants are volatile organic chemicals and can catch fire or explode, especially when combined with smoking. As with many other drugs, users may also injure themselves due to loss of coordination or impaired judgment, especially if they attempt to drive.