Which of the following symptoms is characteristic of the depressants' effect on the body?

The characteristic symptom of depressants' effect on the body is indeed constipation. Depressants, such as alcohol, benzodiazepines, and barbiturates, work by slowing down the central nervous system. This slowing can lead to various physiological effects, including reduced muscle activity and a slowdown in digestive processes. As a result, individuals using depressants may experience constipation due to decreased gastrointestinal motility.

In contrast, the other symptoms listed are not associated with the effects of depressants. High alertness is typically linked to stimulants rather than depressants, which induce relaxation and drowsiness. Feeling of euphoria can occur with some substances, but that is often more related to stimulants or certain psychoactive drugs rather than the general effects of depressants. Increased heart rate is also against the typical effects of depressants, as they generally cause a decrease in heart rate due to their relaxing impact.