Can Valium and nubain be used together?

Very carefully. Yes, benzodiazepines (like valium) can be co-prescribed with opioid analgesics (like nubain), but only under the watchful eye of a physician. These two classes of medications can be very harmful--even fatal--in combination, as the two classes of medications potentiates the effect of the other. Many people die from this combination of medications, so only take if a physician has prescribed.