I think true physical dependency to GHB doesn't form in any significant sense if taken only once, at night. There may be a rebound of sorts, but nothing like taking say diazepam 1x a day (which can produce profound dependency).
It's alot like alcohol. If one drinks a few drinks every night in the evening and only in the evening, they don't develop a physical addiction. I even surprised myself when I stopped my nightly heavy drinking, when I quit my 200ml habit of drinking tanqueray (which is stronger than vodka, being nearly 50% alcohol by volume). I stopped suddenly after years, and to my surprise, no physical withdrawal. Just some difficulty sleeping. And I'm sensitive to GABAergic withdrawal, having been addicted to benzos in years prior. I drank that entire dose of gin in a single drink, once a night, and all that 200ml within the course of maybe 15 minutes (with some ice, and maybe 200ml of sparkling water). Each night that one drink would consistently get me pretty fucked up. So I was quite surprised, given how wrecked that nightly "dose" of gin got me, that when I suddenly stopped cold turkey after years of that, no physical withdrawal was apparent. Now, say instead of that monster nightly gin sledgehammer, I had spit that 200ml into 6 divided doses every 4 hours (so like ~35ml every 4 hours, which is one shot) I bet the consequence would have been far worse due to the constant 24/7 blood levels.
GHB, alcohol, carisoprodol and a few other atypical gabaergics appear to be the same way; you really need to take them round the clock to develop a true physical dependency. I also expected bad things to occur I cold turkey'ed a 6 to 8 month run of 2 grams of carisoprodol every single night, also all in one dose. But when I suddenly stopped no physical dependency was apparent, again maybe trouble sleeping, but nothing like benzo withdrawal or delirium tremens.
Benzos are a very different story however, given their tendency to have long-term desensitizing effects in GABA-A receptors, and their ultra high specificity and potency aimed at one little pocket on the GABA-A receptor complex (within which are itself a few different binding sites). That, and their extended duration of action and in some cases their even longer acting metabolites, leads to physical dependency from even 1x a day dosing. Though I've never gone through z-drug withdrawal (zolpidem, etc.), I would imagine that despite their short acting nature, even 1x a night dosing over long periods of time could produce withdrawal symptoms due to their ultra high specificity for the alpha-1 benzodiazepine receptor subtype. By comparison, alcohol acts more broadly and less specifically, and is of low potency (just like GHB and carisoprodol, short-acting drugs whose doses often can be measured in grams, rather than milligrams like benzos).
But no question, if you dose GHB every 5 hours however, you'll find yourself in a world of hurt however. Same goes with alcohol and carisoprodol.
