Substance refers to a chemical that alters a person's mood or behavior when it is smoked, injected, drunk, inhaled, or swallowed in pill form.

In the psychology context, a substance can refer to a chemical substance, such as a drug or medication, that is ingested or otherwise introduced into the body and can have an effect on a person's thoughts, emotions, and behaviors. Substances can be legal or illegal, and they can be used for a variety of purposes, including recreational, medicinal, or performance-enhancing.

Examples of substances that may be used in the psychology context include:

Substance use and abuse can have a range of effects on an individual's mental health and well-being, and can sometimes lead to substance use disorders, which are characterized by a pattern of problematic substance use that leads to significant impairment or distress. Substance use disorders can be treated with a combination of therapy, medication, and support from family and loved ones.