You'd die of asphyxiation before the THC. Basically, you'd need to inject pure thc into your veins to reach the concentration necessary to OD.

https://www.deadiversion.usdoj.gov/fed_regs/notices/2001/fr0418/fr0418h.htm

Although a median lethal dose (LD50) of THC has not been established in humans, it has been found in laboratory animals (Phillips et al., 1971). In mice, the LD50 for THC was 481.9, 454.9 and 28.6 mg/kg after oral, intraperitoneal, and intravenous routes of administration. In rats, the LD50 for THC (extracted from marijuana) was 666.0, 372.9 and 42.5 mg/kg after oral, intraperitoneal, and intravenous routes of administration. Another study examined the toxicity of THC in rats, dogs and monkeys (Thompson et al., 1972). Similarly this study found that in rats, the LD50 for THC was 1140.0, 400.0 and 20.0 mg/kg after oral, intraperitoneal, and intravenous routes of administration. There was no LD50 attained in monkeys and dogs by the oral route. Over 3000 mg/kg of THC was administered without lethality to dogs and monkeys. A dose of about 1000 mg/kg was the lowest dose that caused death in any animal.

...

In humans, the estimated lethal dose of intravenous dronabinol [(-)-D9-THC] is 30 mg/kg (2100 mg/70 kg). In antiemetic studies, significant CNS symptoms were observed following oral doses of 0.4 mg/kg (28 mg/70 kg) (PDR, 1997).

A 100kg (220lb) person would need roughly 3 grams of pure THC injected into their veins to OD. THC is pretty effective at even 1/100th of that amount.