Hi.. Can understand your concern.. As per your query first of all Gabapentin which is more commonly used as an ANTI-CONVULSANT and ANTI-EPILEPTIC DRUG used to control seizures and it is used to treat pain only in specific conditions like NEUROTIC PAIN (NERVE PAIN) caused in Shingles that is a herpes zoster infection or other nerve induced pains. In case of dental pain it is not indicated and other drugs like Ibuprofen, tamadol, ketorol DT are commonly given.. The other part of the query is that TAKING AN EXPIRED OR OUTDATED DRUG IS COMPLETELY NOT RECOMMENDED as after the shelf life of drug is over there can be degradation of the drug and the products formed after degradation can cause toxic effects on the body leading to organ failures and at times even death in severe cases. In some drugs only the efficacy reduces but in others it can have lethal side effects. You should never take such a risk and can take any of the above mentioned painkillers to cure pain. Hope your query is solved.. If you find the answer helpful please write a positive review and click on find this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora.