How long does it take for a cortisone injection to leave the system. My father75 years old has been on valium for many years and has had several hospital admission whilst trying to withdraw he has now down to 4mg daily which he had a good quality of life on however after receiving a cortisone injection 2 weeks ago in his knee he has lapsed back to what he went through years ago and has severe panic attacks on a daily basis which last all day and he basically does not want to go out is pacing the floor constantly throughout the day into the night and is extremely anxious. Doctors advised to double his previous dose of medication however we are unsure if the cortisone in his system is counteracting this as it does not seem to have any affect