St John's wort is an herbal product used in the treatment of mild to moderate depression
It acts by inhibition of reuptake of certain neurotransmitters
Studies have shown that St John's wort can cause multiple drug interactions, even with beta blockers(the medication propranolol
you are taking belongs to the class of beta blockers)
As a result, there is increased metabolism(breakdown) of those drugs in the body, due to which the beneficial clinical effect of propranolol may get reduced.
So...it will be better to consult your treating physician before starting it.
Wishing you a Good Health. Let me know if I need to clarify further.
Thanks & take care.