I thought about TPA but what about a huge amount of good old salicylic acid?
Still not quick enough,,,,,and aspirin is very tart, large doses would be detected....the vinegar sublimation fumes would be noticeable!
This is very exotic. As an ICU RN, I know that heparin has quick onset of action but its half life is very short...perhaps a weaponized powder in large doses could sicken folks quickly as it could be absorbed through the mucous membranes...but it would be destroyed in the stomachs, and with a half life of 30-60 minutes it would have to be a wopping dose and... there would have to be a precipitating insult...say a weakened vessel with hypertension or a GI excoriations for any bleeding to ensue...