To treat high levels of cortisol you need to treat the kidney. Warming and toning the kidney is the most effective method.
This treats the cause rather than artificially lowering cortisol such as certain supplements which should not be used. Schizandra is not an effective way of doing it IMO.
The best herb is Tu Zi Si (Dodder seed).
Siberian Ginseng does sensitize the body to cortisol which causes a lowering of levels. It also shuts off the alarm reaction which can prevent triggers for anxiety.
Tu Si Zi tones the kidney energy which is very helpful as the Kidney Qi/Chi needs to be improved if the nervous system is to be healed. This shows as rings in the iris of the eye through the kidney zone. When taking Tu Si Zi for extended periods these rings widen and become less deep. This is needed if the nervous system is to be healed as the rings prevent healing. This is why anti depressants never provide a cure or lessen anxiety or depression, they never heal anything!
BTW Tu Si Zi is often used with Gou Qi Zi (Goji berry/Wolfberry).