What causes high cortisol levels?

Stress,depression...: Most commonly cause high cortisol level in am and rarely a condition called cushing's disease.

Stress: Cortisol is a stress hormone, released by your adrenal cortex when needed to combat stress. Cortisol has anti-inflammatory properties. The stress that causes cortisol release can be immune system stress, hormonal imbalances, nervous system stress, poor diet....Anything that your body perceives as being harmful can cause release of cortisol.