Indirect-acting agents are substances that enhance the effects of neurotransmitters without directly binding to their receptors. Instead, they work by increasing the availability or activity of these neurotransmitters in the synaptic cleft. This can lead to prolonged or intensified signaling in the nervous system. Common examples of indirect-acting agents include certain antidepressants and stimulants. These agents can increase levels of neurotransmitters like serotonin or dopamine, which play crucial roles in mood regulation and alertness. By modifying neurotransmitter dynamics, indirect-acting agents can help manage various medical conditions, including depression and ADHD.