Reading the wiki page, it seems like the amount that Jesse put in the cigarette should be enough for a lethal dose. Looks like it's at least 20 mg
When the LD50 of ricin appears to be in the region on 2 ug/kg (~0.001 mg/lb), the small vial would be more than enough to take out a few folk! Granted, that is through injection, would need ~10x as much for inhalation and ~10,000x as much for oral consumption.

