Trazodone is a relatively fast-acting drug that usually takes effect within 1 to 2 hours. If your dog takes Trazodone for stressful events, you’ll likely notice them calmer and less stressed within that 1 to 2-hour timeframe. However, if your dog takes Trazodone for generalized anxiety or other behavioral disorders, it may take a few days before a noticeable improvement is made. Your veterinarian will discuss what to expect when starting Trazodone.