i need advise , im planning to get a new domain name for my pharmacy blog site using drug brand name in a Domain is considered spam or be banned in google ? example: viagra dot com or Xanax online dot com etc..
You can do whatever you want. However the are always consequences. If you register a trademark name the trademark owner can have you shut down or take it from you. The answer to you second ? is no. Google sex dot com. Do they look banned to you?
You can not use a Trademarked name in a domain that will be in the same field as the Trademark holders TM. Since you are wanting to use Trademarked drug names for a pharmacy blog then that would be in the same field as the Trademark holders TM is in so it's a TM violation and you can get the domain name taken from you through a UDRP and might also see legal action. The drug companies can be aggressive when it come to protecting their Trademarks so this is a field that you don't want to mess around in.
You can use any name, but be ready, if owner of trade mark will find this - he can write a complaint to registrator, and they will close your domain name.