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Principles Of Drug Addiction

Updated on March 28, 2013

Drug addiction is a growing problem and cause for concern in most parts of the world. This article outlines the basic pharmacological principles of drug action in addiction, with emphasis on psychoactive drugs i.e. drugs that influence subjective experience and behaviour by impacting and acting on the nervous system.

Drugs are usually administered in the following four ways: By ingestion, by injection, by inhalation or by absorption through the mucous membrane of the nose, mouth or rectum.

The route or way of administration of drug influences the rate and degree at which the drug reaches the sites of action within the body.

Oral Ingestion:

The oral route is the preferred route of administration for most drugs. After the drugs are swallowed, they dissolve in the stomach fluids and are passed into the intestine from where they are absorbed into the blood stream. However, some drugs easily pass through the stomach walls and these have a quicker 'hit' or effect as they do not need to reach the intestine in order to be absorbed.

Drugs that are not easily absorbed from the digestive tract or that are broken down into inactive metabolites before they can be absorbed have to be taken through some other route instead of the oral one.

The main advantage of the oral route of drug administration over other routes is the ease and relative safety of this method. However, it can be unpredictable as well. This is because absorption from the digestive tract into the blood stream can be influenced by factors such as the amount and type of food in the stomach - factors that are difficult to determine or measure. Lastly, people with sensitive stomachs may find it quite unpleasant to swallow drugs as this can cause nausea or cramping.



This is a common method of drug administration in the medical profession because the effects are quick, strong and predictable. Drug injections can be administered:

  1. Subcutaneously - i.e. into the layer of fatty tissue just beneath the skin
  2. Intramuscularly i.e. into the large muscles of the body
  3. Intravenously i.e. directly into veins at points where they run just beneath the skin

Many drug addicts prefer the intravenous route because the bloodstream directly and quickly delivers the drug to the brain. This produces a strong, heightened effect called the 'rush" which is often missing with other routes of administration. It is also a more efficient method of taking the drug as a small amount is enough to produce the effect, hence less drug and less cost in incurred. Lastly, injecting drugs does not damage the lungs and mucous membrane which smoking (snorting) can.

However, with this method of drug administration there is very little opportunity to counteract the chances or effects of an overdose or an increased addiction. Needle sharing, poor hygiene and lack of proper injecting technique can raise the likelihood of infection. Prolonged IV drug use and the use of blunt injections can lead to scarring of peripheral veins or even arterial haemorrhage.



Some drugs are absorbed into the bloodstream through the network of capillaries in the lungs. Many anaesthetics are typically administered through inhalation, as is tobacco and marijuana. The disadvantage of this method is that it is difficult to regulate the dose of the inhaled drug, hence one can easily overdose. Also, chronic inhalation or smoking can damage the lungs.

Some of the drugs can be administered by absorption through the mucous membranes of the nose (snorting), mouth and rectum. However, prolonged use can result in damage to the membranes.

Recreational drugs (e.g. cocaine) that are commonly inhaled can easily harm the nasal cavity and can even destroy the nasal septum. This is because of the extreme constriction of blood vessels inside the nose in the process or the drug itself may be caustic. It is also possible to get infected with Hepatitis C by sharing contaminated tools.


Mechanisms Of Drug Action:

Psychoactive drugs can influence the nervous system in a number of ways. Some drugs act diffusely on the neural membranes throughout the Central Nervous System. Other drugs bind themselves to specific synaptic receptors or influence the synthesis, transport, release or deactivation of particular neurotransmitters. They can also influence the chain of chemical reactions elicited in postsynaptic neurons by activating their receptors.

Drug Addiction:

Not all habitual drug users are addicts. Addiction results when habitual users continue using a drug despite its adverse effects on their health and social life and even after repeated efforts to stop using it (Volkow & Li, 2004)

People addicted to drugs sometimes take drugs to prevent or alleviate the withdrawal symptoms of drugs, but this is not the major motivating factor in their addiction. This is why most addicts renew their drug taking even after months of enforced abstinence or after their withdrawal symptoms subside.

Effects of Drug Addiction on Brain Circuits
Effects of Drug Addiction on Brain Circuits | Source

Impact Of Addiction

  • Intensification of desire for the drug
  • Loss of voluntary control over behaviour
  • Heightened sensitivity to cues associated with the drug - sights, sounds, smell and taste
  • Reduced sensitivity and responsiveness to other rewarding stimuli
  • Dopamine receptors become less sensitive to stimulation
  • Long term changes in decision-making, learning and memory

Drug Tolerance:

Drug tolerance refers to a state of decreased sensitivity to a drug that develops as a result of repeated exposure to it. Drug tolerance can be seen when a given dose of the drug has less effect than it did before drug exposure or when it takes more of the drug to produce the same effect. Thus, there is a shift in the dose-response of the individual to the drug i.e. greater dose is required to produce the same effect.

Motivations Behind Addiction:

To alter mood

To regulate emotions

To experience pleasure

To soothe overwhelming pleasure

Way to manage trauma, stress, anxiety or depression

Used for alleviating unpleasant feelings

Coping strategy to disconnect from pain

Drug Withdrawal Effects And Physical Dependence:

Withdrawal Syndrome means an adverse physiological reaction triggered off in the body by the sudden elimination or withdrawal of a drug after it's been in the body for a significant amount of time. The withdrawal effects of the drug are completely opposite to it's initial effects. A person is said to be physically dependent on a drug if he suffers from withdrawal symptoms after he stops taking the drug.

The intensity and severity of the withdrawal symptoms depends on the type of drug being used, the duration of usage, degree of exposure and the speed with which the drug is eliminated from the body. The longer the exposure to a greater dose, followed by a rapid elimination, the more severe the withdrawal effects.

Addiction - Psychologically Complex:

Addiction is a complex area and studies of addicted patients have found that they differ psychologically from healthy controls in a number of ways. It is therefore important that efforts to develop theories of drug addiction and effective treatment must take these psychological differences into account.

Lastly, addiction is not limited to drugs but several other behaviours exhibit the defining characteristics of drug addiction. Regardless of the object or behaviour one is addicted to, addiction impairs voluntary control and reinforces impulsiveness and instant gratification in a person. Addiction impairs decision making, prevents planning as well as awareness of actions and behaviour. Eventually, it leads to long-term changes in the brain that can have detrimental consequences for the addictive individual.

A Useful Video On Drug Addiction:


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