As with any drugs you should only take these drugs together while under the supervision of a physician. Because both these drugs suppress central nervous system functioning they are listed as having a 'moderate' interaction with each other. Taking too many of these drugs together can make you drowsy and uncoordinated and, in a worse case scenario, put you into a sleep you might not awake from. Never take alcohol with either of these drugs.
This is the warning the Drugs.com Drug Interaction checker provides about using these drugs together. http://www.drugs.com/interactions-check.php?drug_list=1770-0,1937-2171
MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients.
MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.