I agree with Mark that St. John's Wort should be avoided completely.

There are other methods of decreasing anxiety that are much better than St. John's Wort.

The latest concussion research has indicated that a great number of people who don't recover within the first year after a concussion are suffering from pituitary gland or stalk damage or dysfunction that was caused by the concussion. Some experts even think that hormonal imbalances are what cause PCS altogether - but that they resolve themselves in most people within the first year after the trauma.

The pituitary gland secretes hormones that humans need in order to function physically and cognitively.

St. John's Wort has proven to interrupt the hormone or endocrine processes which effects the hormones that humans need for cognitive and physical functioning in addition to it affecting other brain systems that should not be messed with, especially not after a brain injury.