What is a therapeutic index (TI for short):

TI is a way of gauging a substance toxicity. It can be calculated in two different ways:

• LD50 / ED50
• TD50 / ED50

LD50: lethal dose in 50% of the test population

ED50: dose to achieve desired effects (in this case experiencing pyschoactivity) in 50% of the test population

TD50: dose to experience toxic effect in 50% of the test population

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In this case all the values are calculated using the first method.

Keep in mind that the substances used are pure and in a lab environment.

Addressing inaccuracies:

As you might imagine calculating the TI of a given substance for humans is pretty hard, this data is based on animal studies and estimates based on death reports, so it might not be incredibly accurate. Also the therapeutic index calculated this way doen't directly measure how toxic a substance is for your body, although a broad therapeutic index generally implies a less toxic substance.

(?): since it's unknown if these substances can cause death in humans it's really hard to calculate their TI

(*): LD50 are all over the place for this substances, this is the best i could find.

Sources: https://pdfhost.io/v/Tdx47N5.G_TI_of_various_drugs

Tool: google sheets

if you find more accurate sources please link them in the comment's

edit: some clarifications