Is it safe to take 4mg of diazepam and 10mg of amitriptyline together at bedtime?

Depends...: That is not a lot of diazepam, but it is a benzodiazepine (tranquilizer)! the Amitriptyline dose is also relatively low, but it is a tricyclic. Be careful when combining any medications; however, if you have been on these medications for a long time, it may not be a big deal. If these are new to you, however, i would be careful taking 2 sedating medications at the same time. It can be done safely.

Were they both : Prescribed by the same doctor? There is a possible interaction with the two of them: potential for dizziness, drowsiness & v concentration. However, if you are taking them & going to bed this should not present a problem.