Your doctor will give you specific instructions for dosage, which include an outline of how often you need to take gabapentin for anxiety. In the manner that Psycom describes the dosage can start low and then increase as time goes by. In the case of anxiety, the dose of gabapentin is usually set at Gabapin 600 every time during the night. The dosage can be gradually increased every three or five days. Some individuals take Gabapin 300/daywhile others take 3,600 mg/day. This is the highest dose that has been that has been approved by FDA.