in modern world medicine this question can be answered in 2 ways -
methods to increase permeability for more effectively delivering drugs and
methods to disrupt BBB and cause anything to enter Brain.
answering them one by one
for 1st - L dopa, mannitol glycerine and an opiod pappeverine
for 2nd - cocaine and some illicit drugs like MDMA.
Next Steps
brain works very smoothly with body dynamics - until unless there is no significant edema in brain, no need to tickle BBB. if there is brain swelling - inj mannitol can be used.
Health Tips
consult a neurologist if you have any other doubt regarding this.