Benzodiazepines losing effect?

[Matt The Funk]

SWIM has a decent history with lots of downers, specifically benzo's, and more specifically alprazolam(xanax) and clonazepam(klonopin). Now SWIM hada decent tolerance at this point in time, but it shouldn't have been too good as he slowly tapered his dosages to get off everyday benzo use, and switch to as needed. SWIM took 1mg klonopin the day before for a dentist appointment. On to the experience....SWIM first consumed some pretty mid quality cannabis(low grade medical quality) and after about a gram he was at where he wanted to be. Next he took 1.5mg klonopin sublingually, and after 15 minutes 5mg valium. Within 20 minutes he was feeling a bit more relaxed(cannabis helps with that anyways) but much less then he was expecting. 20 minutes later he then proceeded to pop 2mg of xanax and smoke a bit more cannabis. Still not feeling the benzo goodness he decided to pop 30mg of valium and smoke even more cannabis, and along with that pop a 5mg pill of ambien(zolpidem tartrate). By the end of the night the only buzz he had really ended up feeling was the cannabis. And once that was over he just decided to get drunk(drank a lot, and usually isn't a drinker).
Now for SWIM's question, WHY DIDN'T HE GET ANY BENZO EFFECT? It makes no sense to him. He barely even got the anti-anxiety effects from them. Is there any pharmalogical answer to this? Or even just obvious answer? Keep in mind SWIM's tolerance was relatively low....