What class of drugs includes illegal substances like heroin and synthetic opioids?

The class of drugs that includes illegal substances like heroin and synthetic opioids is categorized as depressants. These substances primarily work by slowing down the activity of the central nervous system. Heroin, for example, is an opioid that not only acts as a pain reliever but also produces a feeling of euphoria, which is why it is misused. Synthetic opioids, which include drugs like fentanyl, are engineered versions of naturally occurring opioids and can be significantly more potent and dangerous.

While prescription drugs can also include opioids, they do not exclusively cover the entire range of illegal substances such as heroin. Stimulants are drugs that increase brain activity, leading to heightened alertness and energy, which contrasts with the depressant nature of heroin and synthetic opioids. Hallucinogens alter perception and consciousness but do not fall within the category of substances like heroin. Therefore, the correct classification for heroin and synthetic opioids is depressants.