The LD50 for cannabinoids is approximately your own weight. At least in the monkeys and rats studied, because there has never been a documented human overdose and proper studies are both unethical and (in the US) illegal.
Basically, a marijuana dry flower overdose would come after A) your lungs were ruined by the enormous quantities of smoke inhaled after a short period or B) you were crushed or smothered under the plant material.