It will heighten the tolerance pretty fast.

Tolerance and dependence of a drug is a trademark of addiction. The tolerance of a drug builds in which case a person needs more of the drug in their system. The dependence on a drug, is the need for the drug in which to feel like you are living a normal life.

Repeated exposure to a stimulus could increase the development of drug tolerance.

The Olympic have a zero tolerance drug policy, Marion Jones was stripped years after she won her medals.

Yes. There are some drug effects for which people CANNOT develop tolerance. Of course there are other drug effects which commonly cause people to develop tolerance. If you have specific drugs and effects in mind, let me know.