How long does it take gabapentin to work for nerve pain when first prescribed ?

Everyone is different. Go to Drugs.com and read about this. Also enter all other meds you are taking in the interaction checker as some can change metabolism of gaba.

Since gabapentin is metabolized in the kidney, very few drug interactions to be encountered, but dose is key, and usually start low and titrate up to get accustomed to potential side effects. Efficacy can be seen from 300mg thrice daily to twice that dose, but cannot achieve further benefit above this. At higher dose, would expect noticeable result at 10-14 days.