Get emergency medical help if you have signs of an allergic reaction to Valium: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Diazepam can slow or stop your breathing, especially if you have recently used an opioid medication, alcohol, or other drugs that can slow your breathing. A person caring for you should seek emergency medical attention if you have weak or shallow breathing, if you are hard to wake up, or if you stop breathing.
Call your doctor at once if you have:
severe drowsiness or dizziness;
unusual changes in mood or behavior;
new or worsening symptoms of depression or anxiety;
thoughts of suicide or hurting yourself;
confusion, hallucinations, sleep problems; or
new or worsening seizures.
The sedative effects of diazepam may last longer in older adults. Accidental falls are common in elderly patients who take benzodiazepines. Use caution to avoid falling or accidental injury while you are taking this medicine.
Common Valium side effects may include:
drowsiness;
feeling tired;
muscle weakness; or
problems with balance or muscle movement.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Valium side effects (more detail)
