LD does stand for lethal dose. But LD50 is different. LD50 means that the stated dose would be lethal to approximately 50% of the subjects who consumed the substance(s). Alprazolam (Xanax) is a potent medicine. I'm actually calmer rn thanks to it. However, it is a triazolo Benzo, and much more potent than most typical Benzos. But triazolo Benzo or typical Benzo, they have a very high Therapeutic Index so the dose between the effective dose & the fatal dose is massive. Some drugs have a very narrow therapeutic index. GHB (sodium oxybate) has a very LOW therapeutic index. The dose that is effective is not much lower than potentially fatal doses. So benzos on their own should never be taken in excess as it only causes sedation & possibly a blackout, which can lead to more serious things happening. I've known of a few people who have died (both intentionally & accidentally) from Methadone + Xanax combination. Methadone does have a very long 1/2 life, tho it's analgesic effects only last 6-8h, it's an active opioid for 24+hrs. It's also subtle, but very potent. It's a good medicine when used correctly, but also an extremely unforgiving drug when used inappropriately.