Association of Social Work Boards (ASWB) Clinical Practice Exam

The presence of dilated pupils and a jittery feeling in a client strongly suggests the use of a stimulant substance. Cocaine is known for causing significant increases in energy, alertness, and physical agitation, which aligns with the symptoms of feeling jittery. Moreover, stimulants such as cocaine commonly lead to autonomic nervous system responses, including pupil dilation.

In contrast, the other substances listed have different effects on the body. Heroin typically causes constricted pupils and a sense of calmness or sedation, not jitteriness. Marijuana can lead to a range of effects but usually does not produce significant jitteriness or dilated pupils in a manner consistent with stimulant use. Painkillers, particularly opioids, generally lead to sedation and can also result in constricted pupils.

Overall, the key indicators of dilated pupils and jitteriness make cocaine the most plausible substance in this scenario, as it is associated with stimulant effects that can heighten anxiety and physical restlessness.