Not sure if there's an actual cross tolerance but in my experience, there seems to be a bit of a "cross tolerance" for all drugs in the same class. Like a person who takes downers all the time..
For example: a lady I was in the psych ward with was a hardcore benzo/opiate/etc abuser. A shot of haldol and ativan, followed by a thorazine shot did nothing to her whereas it would incapacitate a regular person.
If you're used to taking downers it might not fuck you up AS bad but take a lower dose at first to be on the safe side.
This may be what's referred to as "learned tolerance" commonly associated with alcohol. Am I making any sense?