Neurontin (gabapentin) is very commonly used for opiate withdrawal during detox in rehab centers. The idea is it is slightly relieving peripheral neuropathic pain, while helping regenerate your neural function.
tolerance goes up rapidly, i believe i was on 600mg 4x day, and there was no real psychoactive effect to speak of, but this is my personal experience.
trying to get high on it isnt the most efficient, and will make you pisss out your ass. also, the way it interacts with GABA it can raise the seizure threshold, and lower the need for benzodiazepene ( benzo part came from prescribing doc, i havent found great evidence on the interwebs, and addition shrinks will tell you anything)