George had started taking cocaine a year ago. he is addicted to the feeling of euphoria brought about by cocaine. of late, even after using the same amount of cocaine that he had been using for the past year, he feels less of its effects. this situation is referred to as

This situation is referred to as tolerance.
George has developed a particular tolerance to the amount of cocaine he used to take before. He doesn't feel the same effects he used to when he started using cocaine, which means that he will probably start using higher doses of the drug in order to feel the same high.