Which syndrome is characterized by a characteristic group of withdrawal symptoms when usage of a substance suddenly decreases?

The correct answer is "Abstinence syndrome," which refers to the withdrawal symptoms that occur when an individual who is physically dependent on a substance reduces or stops its use. This syndrome can manifest through various physical and psychological symptoms, depending on the substance involved.

When someone has been using a substance regularly, their body may adapt to its presence, leading to physical dependence. If the substance is suddenly decreased or removed, the body can react adversely, resulting in withdrawal symptoms. These symptoms can include anxiety, irritability, tremors, nausea, and in some cases, severe complications that can pose health risks.

The other options relate to substance use, but they serve different contexts. Tolerance refers to a diminished response to a substance after repeated use, meaning more of the substance is needed to achieve the same effect. Substance dependence involves both a psychological and physical reliance on a substance but does not specifically pertain to the immediate withdrawal symptoms when the substance is stopped. Substance abuse involves a pattern of harmful use of substances leading to significant adverse consequences but does not specifically focus on the withdrawal process.