An individual with opioid use disorder is released from jail after 3 months of incarceration. She returns to her old neighborhood and purchases heroin and injects herself with the 'usual' amount of drug she had habitually taken. She then collapses and becomes unconscious with shallow respirations within 1 minute of use. The most likely cause is a(n):
Reaction to a contaminant in the heroin
Increased drug purity
Loss of tolerance
Interaction with another medication started while incarcerated
