No real candidates for that. Also there is no documented human death by LSD, even though there were some candidates that had plasma levels of 1000-7000µg (!!!) per 100 ml blood (!!!!) and were in comatose states but all survived with no residual effects. I couldnt find any LD50 for DMT, and this substance is also considered very safe in use for humans, except for people with underlying psychiatric problems. Psilocybin cubensis' (mushroom that contains psilocybin and psilocin) LD50 for a 68kg/150lbs person is considered to be 3015g which is a ridiculous amount to consume. Hallucinogens in general are not a good choice for that. You are better off with opiates or opioids to induce respiratory failure.