The substances producing changes in behaviour are called as “psychoactive drugs.” Repeated administration of a psychoactive drug can result in tolerance or sensitization.
Tolerance is the decreased response of the body towards the drug with repeated administration. Means, the patient needs more quantity of drug to produce the same therapeutic response as before. Tolerance resembles habituation.
Sensitization response is the enhanced response to some stimulus, which is opposite of habituation.
Thus, the blanks can be filled with tolerance; sensitization.