300 mg of gabapentin is a low daily dosage. I have been taking 1200 mg/day for the past 8 years and have experienced absolutely no side effects. Abruptly ending your daily 300 mg intake of gabapentin should not be a problem, but if you're really concerned about it, taper off your daily intake by ingesting a 300 mg capsule every other day instead of every day for a couple weeks before stopping altogether.