How could a heroin overdose cause acute respiratory distress syndrome (ards)?

Toxic insult to lung: Aspiration, pneumonia, near-drowning, toxic inhalation and lung contusion are listed among the direct injury risk factors for ards. If the heroin dose is large enough to depress breathing and cause GI tract spasms, it is possible that the body may aspirate and cause injury to the lung parenchyma.

Extreme danger: Heroin overdose is an extremely dangerous situation. It can cause the heart to stop, blood pressure to collapse, shock, major injury to all vital organs including the lungs.

Leak: Heroin itself, as well as the many substances used to "cut" the heroin (think of it like the drug dealer watering down the drink, only ts the heroin being diluted, usually with talk, but any white powder, even bleach) can all cause direct injury the lung's blood vessel and lining, resulting in leak of plasma and fluid into the lung. This is exactly what ARDS is, pulmonary edema from leaky vessels.

Possible: Vomiting and aspiration can cause ARDS and is the most frequent cause in heroin od. Sometimes direct toxicity from adulterants in heroin can cause an acute lung injury.