Gez - This is probably too late, but here goes.

Neurontin (gabapentin) is a medication that was originally used as an anticonvulsant. Now it has been used successfully in treating various, seemingly unrelated disorders, such as social anxiety, chronic fatigue syndrome, fibromyalgia, migraines, peripheral neuropathies, phantom limb pain, generalized anxiety disorder, panic attacks (though I haven't seen it do much good in panic disorder). It is one of those medications that either works or it doesn't. There doesn't seem to be any middle ground.

The half-life of Neurontin is only about 6 hours, so technically it needs to be taken 3 or 4 times daily for full effect (at least when used as an anticonvulsant). In many of the disorders above, many people can get away with taking the drug once or twice a day. This suggests to me that the Neurontin is affecting some neuronal pathway in the brain, acting as sort of a switch or block (I really dunno); this would be a slightly different mechanism of action from that when used in epilepsy.

As for your friend, I'd say that there is something going on that is possibly not related to the Neurotnin. A doc would have to rule out a number of different causes for his cognition problems. This could be something stressful in his life, a major depressive episode, recreational drug use, too many wobbly pops (barley sandwiches; ales), a miny stroke, or some other medical condition. I do not think that the Neurontin is to blame for this, although it can cause some cognition problems when first starting the medication. This usually only lasts until one's body becomes adjusted to the drug.

Some other interesting notes about gabapentin. It is not metabolised, but is excreted in the urine unchanged. There are very few clinically significant drug-drug interactions with Neurontin; I do think it affects the levels of some other anticonvulsants, but which those are eludes me right now.

Also, Neurontin is absorbed from the intestinal tract by an active transport mechanism. This is different from most substances that are absorbed into the body via osmosis or diffusion. This active transport mechanism can become saturated rather quickly. The system is supposed to be saturated at doses of 600mg; anything more is not absorbed (yes, I know that there is an 800mg tablet ... go figure). This can really become a pain if one is taking 4800mg a day. That would mean that to get full effect of the 4.8g a day, one would have to take 600mg eight times a day. I learned this from the noted pharmacologist, Larry Ereshefsky, out of Texas (I believe).

Anyway, let us know what they figure out is going on. They should have resolved the problem, or at least ruled out several potential causes for the cognition problems.

Sorry, that's all I got. - Cam