Are you interested in learning about the side effects, or are you just asking if it does any long-term damage to the brain/body?
Even if you don't have a lethal overdose, you can still get some nasty side effects. I have taken care of friends who were on GHB and were completely impossible to communicate, unaware that I was there, and doing crazy stuff like smashing their head on the floor over and over. Renz Envy listed many of the other side effects above. I don't agree that the side effects are solely caused by poorly produced GHB.
As for long-term effects, it depends how often you use it (and also on how it was made, how pure it is). In multiple animal studies, GHB has been found to be neurotoxic, reducing the number of neurons in the brain, and impairing things like learning and memory. Of course this is much more pronounced with chronic use.
I don't know whether or not it does any lasting damage to organs or not, but I wouldn't be surprised if it did. I can try to find out if you want. I've also heard if the pH is too high or too low it can cause damage.
Aside from mental addiction, GHB can also cause physical dependence, causing withdrawal symptoms when the person stops using it.
I would say if you're going to use it be very careful with the dose, start with a low dose, try to get as reliable a supply as possible, test the pH, and only use it once in a while, in order to try to minimize harm.
Whether you are the GHB hobbyist or troubled addict, it is always best to test. pH strips can indicate a good solution from a poor one.
The pH of safe GHB liquid is generally between pH 6 and 8. You can use pH papers to test the acidity/alkalinity of their products and
I've heard if it is too basic you then add a little lemon juice or vinegar to adjust the pH to close to 7.5, which is said to be ideal. Do you agree?