1.   This barrier is a complex structure that prevents many drugs and chemicals in the blood from entering the brain.

2.   The bullet had entered his brain.

3.   Although hypericum has been around since before Christ, seems incredibly safe and is natural, once it enters the brain it still acts like a drug.

4.   As the oils are absorbed into the bloodstream, they enter the brain and trigger various chemical reactions.

5.   But if the virus enters the brain, it can paralyze the muscles used in swallowing and breathing.

6.   But weeks later, when the parasites enter the brain, patients begin hallucinating or acting wildly.

7.   Caffeine enters the brain very rapidly and stays active for several hours, but its effects drop off more quickly than those of some other stimulants.

8.   It allows less cocaine to enter the brain, thereby reducing the euphoric effects of the drug.

9.   It enters the brain through the nasal tissues.

10.   One of the two bullets fired at him fragmented in his skull but did not enter his brain, and he was released after five days in the hospital.