Hi, Valium contains diazepam which belongs to the group of medications known as benzodiazepines is used to treat anxiety, alcohol withdrawal symptoms, skeletal muscle spasms, seizures, insomnia etc. Again, Trazodone belongs to the group of medications known as serotonin modulators which is used to treat depression, insomnia etc. Using Valium with Trazodone may increase side effects like dizziness, drowsiness, confusion and difficulty in concentrating. Some people may also experience impairment in thinking, judgement and motor coordination. Your son should avoid activities requiring mental alertness like driving or operating hazardous machinery until he knows how these medications affect him. So, before giving someone or taking such type of combination of medications, someone should consult his doctor. Take care. Hope I have answered your questions. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician