Pharmacology - Do you only get GBL/GHB withdrawals from 24/7 dosing?

[Synesthesiac]

I've been scouring the forum and its obvious that chronic 24/7 dosing for weeks causes bad withdrawals when stopped cold turkey, however I'm a but confused as GHB (Xyrem) is prescribed to people to use nightly so they can get to sleep. And presumably they dont get withdrawals at all? So once nightly use is okay, but multiple daily dosing is not?

I ask as my friend has gotten into a habit recently of using GBL in the nightime before he goes to sleep, he's been doing this for about seven days now. He is having a diluted 3ml glass of GBL which he drinks slowly every night at the moment, but never drinks it in the day or mornings. I know that he should be using NaGHB instead of GBL but he cant perform the synthesis at the moment for various reasons. So far he has noticed no detrimental effects, and just enjoys his drink of GBL most nights like people do with alcohol. Plus it helps him nod off and keep a good sleep routine.

Will there be any detrimental effects or addiction/withdrawal issues if this pattern is continued? Do other people use GBL like this? (nightly but not 24/7)