Understanding Tolerance in Psychoactive Drug Use

Consider the following scenario: A 45-year-old male individual has been experiencing chronic pain due to a medical condition for the past several years. His physician has prescribed a combination of medications including an opioid analgesic for pain relief and an antidepressant to help manage his mood. Over time, the patient begins to notice that he requires higher doses of the opioid to achieve the same level of pain relief, despite not having changed his physical condition. Additionally, he sometimes feels an intense craving for the opioid, even when his pain levels are controlled.

Based on this information, which psychoactive drug-related phenomenon is this patient most likely experiencing?