Does gabapentin cause a false positive on a urine drug test?

Not Likely. It is unlikely that Neurontin (Gabapentin) will trigger a false positive urine test for drugs. However, if you are taking other medications then these medication may alone or in combination with Neurontin trigger a positive urine screen. Also, poppy seeds and other foods, fermented or otherwise may result in positive screen. Here's a reference: http://dig.pharm.uic.edu/faq/2011/Feb/faq1.aspx.
No, irrelevant. Gabapentin, a relatively new anticonvulsant compared to carbamazapine and phenytoin, differs from most other anticonvulsants because it has minimal drug interaction potential and is not metabolized in humans.