"Indirect-acting" refers to a mechanism where a substance influences a biological response without directly binding to a receptor. Instead, it may enhance or inhibit the release of neurotransmitters or hormones, leading to an effect. This approach is often seen in certain medications that modify the activity of the nervous system or other bodily functions. For example, some antidepressants work indirectly by increasing the levels of serotonin in the brain, which helps improve mood. By affecting the underlying processes rather than targeting specific receptors, indirect-acting agents can produce broader and sometimes longer-lasting effects.