Which of the following is a common defense mechanism used by individuals with substance use disorders?

Rationalization is indeed a common defense mechanism employed by individuals with substance use disorders. This mechanism involves creating logical explanations or excuses to justify their actions or feelings, especially when it comes to their substance use. For instance, a person might rationalize their drinking by saying that it's a way to cope with stress or that they can stop whenever they want. This allows them to avoid confronting the reality of their addiction and the negative consequences it brings, thus providing a buffer against feelings of guilt or shame.

The other options, while relevant in discussions about behavior and motivation, do not function as defense mechanisms in the context of substance use disorders. Positive reinforcement refers to encouraging a behavior by providing a reward, while self-actualization is related to achieving one's potential and personal growth. Behavior modification focuses on changing specific behaviors through various techniques and does not serve as a way to justify actions that individuals may feel guilty about. Therefore, rationalization stands out as a critical defense mechanism indicating the complexity of psychological responses to addiction.