Nitrites are used as sexual enhancers by 'Poppers'. Main AE is methemoglobinemia, a life-threatening condition. Methemoglobinemia is suggested in the patient with slate-grey cyanosis that does not improve with oxygen therapy, low or spurious SpO2, normal measured PaO2, and chocolate-brown arterial blood that does not turn bright red when agitated in air or bubbled with oxygen. Oxygen therapy and methylene blue are treatment options. Hyperbaic oxygen therapy is reserved for severe or recalcitrant cases. There is a huge list of causal drugs in addition to inhaled nitrites (see under XIV: Acquired Hemoglobinopathies)