Compounds acting on opioid receptors in the body, whether naturally occurring or syntheticThese are drugs made of artificial chemicals rather than natural ingredients. Some of the more popular ones include Ecstasy, LSD, and methamphetamines. More. Their use can lead to the development of crippling physical dependenceWhen the body of a user adapts to functioning with the drug, this can have serious consequences. An ever-larger quantity is needed to feel the same high. It also complicates rehab as detox is required and withdrawal symptoms can be highly uncomfortable. More. Whether used through a prescription for pain management or recreationally, its overuse in the United States has been classified as a national crisis.