How Continued Drug Use Leads to an Overdose

People begin taking drugs like amphetamine for a number of reasons. Sometimes drugs are originally prescribed by a doctor to treat a medical condition. Sometimes people begin using drugs to manage negative emotions and to escape from the difficulties of life. Often, people originally begin using drugs out of curiosity or a desire to be part of a group.

Whatever the reason, the first use of a psychoactive drug is often a very powerful experience. People may feel euphoric or extremely relaxed and comfortable. The experience is generally rewarding enough to prompt further use.

Neurotransmitters and Drugs of Abuse

Different drugs act differently in the body, but their primary effects tend to be related to the way in which they affect neurotransmitters in the body. Neurotransmitters are body chemicals that help cells communicate with each other. A nerve releases a neurotransmitter which travels across the synapse, or gap between cells, and a receptor on a nearby cell receives it.

Scientists have identified more than 100 neurotransmitters, but a handful seems to be responsible for the majority of drug effects. These include GABA, serotonin, norepinephrine, glutamate and endogenous opioids. Dopamine is the body’s primary feel-good neurotransmitter, part of the brain’s reward system, and all drugs of abuse appear to affect it.

How Drug Tolerance Develops

The human body is an intricate machine with much innate wisdom. When it senses that things are out of balance it adapts, in an attempt to maintain homeostasis or balance. When drugs like amphetamine raise neurotransmitter levels abnormally, for example, it attempts to compensate, generally by producing less of a given body chemical or by making receptor cells less sensitive. As the body adapts to a drug’s effects, tolerance begins to develop. When people develop drug tolerance, they need larger amounts of the drug to achieve the same effects a smaller dose once produced.

Any given drug may produce different effects in the body, and tolerance to these effects may develop in different ways and at different rates. The Merck Manual notes that tolerance often develops because liver enzymes involved in metabolizing a drug become more active, and metabolism of the drug speeds up.[1]

They also note that the number of cell receptors may decrease or that strength of the bond between the receptor and the drug may diminish.

The National Institute on Drug Abuse (NIDA) notes that tolerance to the painkilling effects of heroin or morphine develops rapidly.[2] At first, when the drugs bind to receptors, a particular enzyme involved with firing impulses is inhibited. After this has happened repeatedly, the enzyme adapts, and cell firing is no longer changed.

Chasing the First High

People who use drugs like amphetamine often talk about chasing their first high. They try to re-create the euphoria and other effects they first felt. Unfortunately, because the body can begin to adapt to a drug’s effects quickly, people often find themselves rapidly escalating the amount of drugs they consume and their frequency of use.

Chasing a high is generally related to falling dopamine levels. Dopamine is naturally released by the body in response to activities that ensure the survival of the human race, such as eating and procreation. Drugs of abuse hijack this reward system. NIDA notes that drugs of abuse can cause the body to release two to 10 times the amount of dopamine that natural rewards do.[3]

Given this fact, it is not surprising that the body adapts. The Addict Science website reports on a study finding that monkeys allowed to consume cocaine for a year were found to have 15 to 20% fewer dopamine receptors. The brains of alcoholics have also been found to contain significantly fewer dopamine receptors than found in the non-alcoholic population.

Drug Tolerance and Overdose

The fact that people develop tolerance to a drug’s rewarding effects means that they tend to increase the amount they consume. Unfortunately, however, tolerance to a drug’s rewarding properties does not mean tolerance to all of its effects. This means that someone can take a drug like amphetamine in an amount that causes only a moderate high or simply causes them to avoid withdrawal symptoms, and the effects on other body systems can be enough to cause a serious or even fatal overdose.

Overdose reactions are related to the type of drug consumed. Most fatal overdoses are caused by the depression of breathing and other body processes. This risk is greatly increased when multiple drugs that depress the central nervous system (CNS) are consumed together or combined with alcohol. Stimulant drugs have different effects and may cause heart attacks or stroke.

A New Life Is Waiting

If you are ready to address an addiction to drugs like amphetamine, give us a call. Our helpline is toll-free and available 24 hours a day. We can answer your questions and assist you in finding a treatment program that best meets your needs. If you wish, we can even check your insurance coverage for you at no cost or obligation. Why not call now? A new life is waiting.


[1]  “Tolerance and Resistance to Drugs,” Daniel A. Hussar, PhD, Merck Manual, Consumer Version,  (January 17, 2016).

[2] “The Neurobiology of Drug Addiction,” National Institute on Drug Abuse, January 2007, (January 17, 2016).

[3] “Drugs, Brains, and Behavior: The Science of Addiction,” National Institute on Drug Abuse, July 2014, (January 17, 2016).