Drugs can be used in many different ways, as detailed below.
People can use drugs to relieve pain or discomfort or to cure or prevent disease. Medication, also referred to as medicine, can be loosely defined as any substance intended for use in the diagnosis cure mitigation treatment or prevention of disease Not all medication is drugs however.
Recreational drug use is the use of psychoactive drugs for recreational purposes rather than for work, medical or spiritual purposes, although the distinction is not always clear. Recreational drug use is the use of Psychoactive drugs for Recreational purposes rather than for work, medical or spiritual purposes A psychoactive drug or psychotropic substance is a Chemical substance that acts primarily upon the Central nervous system where it alters Brain Recreation or fun is the expenditure of time in a manner designed for therapeutic refreshment of one's Body or Mind. Employment is a Contract between two parties, one being the employer and the other being the employee. Medicine is the art and science of healing It encompasses a range of Health care practices evolved to maintain and restore Human Health by the Spirituality, in a narrow sense concerns itself with matters of the Spirit, a concept closely tied to religious belief and Faith, a transcendent reality At least one psychopharmacologist who has studied this field refers to it as the 'Fourth Drive,' arguing that the human instinct to seek mind-altering substances has so much force and persistence that it functions like the human drives for hunger, thirst and shelter. Hunger is a feeling experienced usually followed by a desire to Eat. Thirst is the craving for liquids resulting in the basic Instinct of humans or animals to Drink. 
The concept of responsible drug use is that a person can use recreational drugs with reduced or eliminated risk of negatively affecting other parts of one's life or other peoples lives. Responsible drug use is a Harm reduction strategy which argues that a person can use illegal drugs or illegally use legal drugs with reduced or eliminated risk of negatively Advocates of this idea point to the many well-known artists and intellectuals who have used drugs, experimentally or otherwise, with few detrimental effects on their lives. Critics argue that the drugs are escapist--and dangerous, unpredictable and sometimes addictive; thus predicating the idea of a responsible use of drugs as an idea, ultimately disputable upon debate.
The gateway drug theory is the belief that use of a lower classed drug can lead to the subsequent use of "harder", more dangerous drugs. The gateway drug theory (also called variously gateway theory, gateway hypothesis and gateway effect) is the hypothesis that the use of soft drugs leads  The term is also used to describe introductory experiences to addictive substances. Some believe tobacco, alcohol, and marijuana are gateway drugs.
Some research suggests that serious drug abusers adopt an atypical drug use sequence with use of other drugs initiated before marijuana or alcohol.  There are many pharmacological similarities between various drugs of abuse. Individual social histories show that "hard" drug users do progress from one drug to another, but the reasons are not clear enough to generalise a gateway. 
Drug addiction is a condition characterized by compulsive drug intake, craving and seeking, despite what the majority of society may perceive as the negative consequences associated with drug use. Drug addiction is widely considered a pathological state. The disorder of addiction involves the progression of acute Drug use to the development of drug-seeking A drug, broadly speaking is any chemical substance that when absorbed into the body 
Drug abuse has a wide range of definitions related to taking a psychoactive drug or performance enhancing drug for a non-therapeutic or non-medical effect. Drug abuse has a wide range of definitions related to taking a Psychoactive drug or Performance enhancing drug for a non-therapeutic or non-medical effect A psychoactive drug or psychotropic substance is a Chemical substance that acts primarily upon the Central nervous system where it alters Brain Some of the most commonly abused drugs include alcohol, amphetamines, barbiturates, benzodiazepines, cocaine, methaqualone, and opium alkaloids. Amphetamine, and related drugs such as Methamphetamine are a group of drugs that act by increasing levels of Norepinephrine, Serotonin, and Dopamine Barbiturates are drugs that act as central nervous system Depressants and by virtue of this they produce a wide spectrum of effects from mild Sedation The benzodiazepines (pronounced, often abbreviated to "benzos") are a class of Psychoactive drugs with varying Hypnotic Cocaine ( benzoylmethyl ecgonine) is a Crystalline Tropane Alkaloid that is obtained from the leaves of the Coca plant Methaqualone is a Sedative drug which is similar in effect to Barbiturates a general CNS Depressant. An opioid is a chemical Substance that has a Morphine -like action in the body Use of these drugs may lead to criminal penalty in addition to possible physical, social, and psychological harm, both strongly depending on local jurisdiction.  Other definitions of drug abuse fall into four main categories: public health definitions, mass communication and vernacular usage, medical definitions, and political and criminal justice definitions.