This chapter talks about psychoactive substances that are commonly misused or abused by older adults. It is important for a psychologist to understand the psychopharmacological dynamics of each substance, how they are administered by an older adult, the symptoms of intoxication and withdrawal, and the psychosocial consequences experienced by the older adult misusing or abusing psychoactive substances. Unlike younger adults, older adults are more likely to avoid illicit substances such as cocaine, heroin, methamphetamine, psychedelics such as lysergic acid diethylamide (LSD) or mescaline, and designer drugs. Historically, the psychoactive substance of choice was alcohol. There are two general types of opioid psychoactive substances: naturally occurring opioids and synthetic opioids. Naturally occurring opioids include opium and its derivatives morphine and codeine, and heroin, which is a chemical manipulation of morphine. Unfortunately, many older adults suffer with chronic pain from cancer, arthritis, or injuries, causing a need for opioid medications.