There are many side effects associated with Gabapentin 300mg, 600mg, 800mg some of them are quite common and can be seen in many people who take the dose but some rare which are rather harmful and can cause severe illness.To avoid the harmful side effects of gabapentin, take the number of capsules as instructed by your doctor. Hence, we can conclude that gabapentin is used for many treatments but it is not appropriate to call it a mood stabilizer.Less serious side effects may include:Dizziness, DrowsinessWeakness, Tired FeelingNausea, DiarrheaConstipationBlurred VisionA headacheBreast SwellingDry MouthLoss of Balance or Coordination