Not telling anyone you know is probably smart. _If_ you write outside of the genre your friends group usually reads and a bunch of them visit and buy your book out of curiosity on Amazon, it can negatively impact the categorization of your books.

"oh these people who usually read historical fiction are buying this new medical thriller. We will show this medical thriller to other people with the same buying habits!"

Only readers of historical fiction who aren't your friends probably won't bother picking up a medical thriller.

Regarding reviews, this is why many authors build ARC teams. Reviews are really important, so they send out advance review copies.