Most of the brain is not hippocampus. You could increase the volume of the hippocampus by taking volume away from the rest of the brain (e.g. making it more dense or taking neurons away from it).
To state the blatantly obvious, if there is a possibility that this drug works by taking neurons away from other parts of the brain, then its use is really dangerous.
BTW is this a guess, or do you have some reason to believe that this sort of neuroplacicity is possible?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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