I’ve rationalized it to myself by saying that drugs are inanimate objects, which aren’t inherently ‘good’ or ‘bad’; it’s dependent upon how you use them. But maybe I’m using that as an excuse because I like the high 
No quotes come to mind off-hand, but I have some thoughts on the matter.
My main concern about that particular drug would be it’s quality. Many years ago when I used it, we would sometimes get “laced weed”, with stuff like PCP in it, and there was a big scare about Paraquat. Do you grow your own or know the source ?
You’re also running the risk of becoming fodder in the “war on drugs”.
Another thought I have about recreational drugs in general, and also the use of mood-altering drugs without rational therapy, is the risk of it encouraging complacency and lowering the objective quality of your life. In the same way that taking pain killers to cover the symptoms of physical problems, without good medical oversight, can lead to bigger problems, drugs that provide “joy”, or that dull the experience of sorrow, without good psychological oversight, can distract your awareness from situtations in your life that could and ought to be improved.
If you value the high enough to take the risks and costs, however, I see nothing inherently wrong with it.
I very strongly recommend you take a much less tolerant attitude toward rationalization. It’s good that you ask us if we think you’re rationalizing, but rationalization is often difficult to detect in ourselves, let alone in others. If you really think you’re rationalizing, I’d recommend seeing a psychiatrist - a couple explicitly Objectivist ones I’d recommend are Dr. Michael Hurd and Dr. Ellen Kenner. At least one of these offer services by phone and even by email.
Lastly, I’m convinced that the dangers of cigarette smoking are wildly exaggerated. They are there, and you should take some precautions if you smoke, but the anti-smoking frenzy today is rife with non-scientific, anti-industrial and collectivist propaganda.