127  Methadone (used to treat heroin addiction)  Efavirenz (used for treating HIV) (some doses of efavirenz can NOT be taken at the same time as VFEND)  Alfentanil and other short acting opiates such as fentanyl and sufentanil (painkillers used for surgical procedures)  Non-steroidal anti-inflammatory drugs (e. g. ibuprofen, diclofenac) (used for treating pain and inflammation)