Then you don't know a lot about drugs. Caffeine can be extremely dangerous in certain quantities. The only drug I know of that has no effective toxicity is cannabis, but that has other possible long term issues.
If you were to refine cannabis down to pure THC, I'm sure it'd have a toxicity level as well. Cannabis, like iceberg lettuce, doesn't have a toxicity level because of chemicals contained in it. And cannabis, like iceberg lettuce, could have stuff extracted out of it which would be toxic in large amounts at high concentrations.
