No deaths due to marijuana overdose.
"There has been no reported case of death from marijuana overdose (not to be confused with overuse; I donít know to what extent marijuana smoke would increase heart disease or lung cancer). The estimated ratio of effective dose to lethal dose for marijuana is between 20,000 and 40,000 to one as compared to between 4 and 10 to one for pure ethanol. This is equal to smoking about 1500 pounds of pot in fifteen minutes. This data has been extrapolated from animal models. (NEJoM, Aug.7, 1997. P. 438)"
http://students.washington.edu/aed/archivemidget/2.htm