I take 600 to 900 mgs. I only take it at night. It has an 8 hour half life so if the effect is needed throughout the day, a 2 or 3 times per day dosage is common.

I don't find any side-effects. I have taken as much as 1200 mgs per dose without a problem. It is important to not take it at the same time as taking a magnesium supplement. Google "gabapentin magnesium" to understand the issue.