A client experiencing yawning, pupillary dilation, and muscle cramps is most likely withdrawing from which substance?

A client exhibiting symptoms such as yawning, pupillary dilation, and muscle cramps is most likely withdrawing from heroin. Heroin is an opioid, and withdrawal symptoms typically manifest in a specific pattern that includes these particular signs. Yawning is often a prominent indicator of opioid withdrawal, reflecting the central nervous system's attempt to regain homeostasis after ceasing use.

Pupillary dilation, or mydriasis, is a classic symptom of opioid withdrawal; as opposed to opioid use, where pinpoint pupils are a common sign. Muscle cramps and aches are also frequent complaints during the withdrawal phase because the body is reacting to the absence of the opioid's effects on the brain and nervous system.

Other substances have different withdrawal symptoms. For alcohol withdrawal, symptoms may include tremors, sweating, and agitation, but yawning and pupils dilating are not typical signs. Cocaine withdrawal is usually associated with fatigue, increased appetite, and sleep disturbances rather than muscle cramps and significant physiological changes like pupillary dilation. Marijuana withdrawal symptoms are generally milder and can include irritability and sleep disturbances, rather than the more severe physical symptoms associated with opioids.

Thus, the combination of yawning, pupillary dilation, and muscle cramps strongly indicates heroin withdrawal.