What are Drugs Tolerance and its effects?

The drugs tolerance occurs when a drug is consumed continuously, resulting in a reduction of their effects on the body. In this way, it is necessary to increase the dose of the substance to re-feel the effects of the substance.

If the person has used opiates regularly enough to experience drugs tolerance, he or she will suffer withdrawal if he stops taking the substance (Carlson, 2006).

Drugs Tolerance

Drugs Tolerance in man

The level of response of the organism to a particular drug depends on two elements:

  • Concentration of the drug in the place where it acts.
  • Sensitivity of the destination of the drug. This is the sensitivity of target cells (and neurons). It depends on genetic factors and adaptive changes of the body. These changes are the body’s response to repeated exposure of a specific substance.

Psychoactive drugs often contain liposoluble chemical compounds that allow them to cross the blood-brain barrier. This barrier is a wall of endothelial cells that regulates substances that enter and leave the brain. Inside this wall is a system of capillaries that offer the brain oxygen and nutrients, while eliminating waste.

It can be said that this barrier protects the delicate chemical system of the brain from foreign or potentially dangerous substances, coming from the blood flow. However, psychoactive drugs can cross this barrier and exert chemical effects on the brain.

Not all substances produce drugs tolerance. Tolerance depends on the chemical composition of drugs and the ability of the brain to differentiate them from their own neurotransmitters. For example, alcohol, illegal drugs, drugs such as benzodiazepines, or substances such as caffeine can cause tolerance.

Psychoactive drugs have the ability to mix with the natural chemicals in the brain. In particular, they interact with neuronal receptors that capture and release neurotransmitters.

Tolerance to the effects of a drug is part of a compensatory mechanism that the brain develops. When the drug begins to exert its effects on the body, the brain detects the existence of an alteration in its balance or homeostasis.

The main response of the brain to this threat to its normal functioning is to resist. To do this, it adapts the receptors and cellular mechanisms to the drug so that it does not take effect.

In short, brain receptors become insensitive to the addictive substance. Thus, the person needs to consume a larger dose of this to feel its effects again.

Differences between tolerance and dependence

When a person repeatedly abuses drugs such as alcohol, hashish, cocaine, heroin, etc., he may develop both dependence and tolerance over time.

Tolerance and dependence are signs that sporadic use of a drug is starting to be problematic. However, there are important differences between dependence and tolerance.

Tolerance develops when a person does not experience the same effects using the same amount of a certain drug or substance. Specifically, what happens is that the brain has adapted to the presence of the drug. Therefore, when a person has a high tolerance, you need to take more frequent doses and more than your friends.

Another sign is that they can start mixing different substances to achieve the desired intoxication. For example, someone who has developed alcohol tolerance will not feel as drunk as before drinking the amount he used to drink. Thus, you will start drinking more quickly or consume more alcoholic beverages. Or, choose strong liquors with high graduation.

However, what he is getting is that the brain continues to adapt to these amounts of alcohol and get accustomed. Needing more and more alcohol to feel drunk.

On the other hand, dependence on drugs occurs when the individual feels that he cannot have a normal life without consuming certain substances. In this way, you need to take this drug to function well in your day to day.

If you do not take it, you will feel the uncomfortable and annoying withdrawal symptoms. The symptoms of withdrawal are often the opposite of those produced by the drug.


Another sign of drug dependence is that the person can spend a lot of time consuming, looking for or thinking about it. Dependence may be accompanied by tolerance when consumption is extended over time.

As the substance is abused, brain cells become more dependent on the effects of the drug. Little by little, they need this substance to maintain a balance in the functioning of the brain. This ends up producing structural damage that leaves cells unable to function properly without the drug.

Finally a vicious circle occurs. As tolerance grows, the dose is increasing and the damage to the brain cells is becoming more serious.

On the other hand, if we talk about other substances like certain drugs, it may be tolerance, but not addiction. For example, tolerance to some effects of prescribed drugs may be developed to suppress pain, without addiction to them. Addiction is some thing like mobile addiction etc.

Types of tolerance

As already described, tolerance affects brain receptors and cells, although other forms of tolerance also exist. According to California State University-Fullerton, there are 3 mechanisms that contribute to increased tolerance (in addition to cerebral tolerance):

  • Metabolic tolerance: this refers to the substances or drugs that are consumed orally. It relates to the rate at which the liver breaks down these substances. When the use is very continuous, this speed increases, staying less time the drug in the bloodstream.
  • Behavioral tolerance: this is the emotional response of the individual according to the expectations he has about the effects of the drug. That is, the person increases the dose voluntarily to obtain more intense effects.
  • Conditioned tolerance: this mechanism increases tolerance through environmental signals. It seems that certain factors in the environment are associated with the desire to take the drug, such as activities, moods, certain sites, situations or people.

These mechanisms attached to cerebral adaptation feed each other, resulting in increased tolerance to the drug.

On the other hand Drug Abuse differentiates three types of tolerance according to the period of time:

Acute or short-term: this tolerance arises from continued exposure to a substance over a relatively short period of time.

An example is what happens with cocaine. With the first dose individuals experience euphoria, increased heart rate and blood pressure. However, with a second dose 40 minutes later, the positive effects of the drug do not increase as expected.

Chronic: This happens when the body adapts to a constant exposure to the drug for weeks or months. The result is that the effects of the drug diminish, needing to take a dose greater than the previous one to re-experience the effects with equal intensity.

Learned: With years of exposure to certain substances, such as alcohol, the person may appear as if he or she has not ingested any substance. That is, the drug no longer works. You can even properly perform activities of your daily life after consuming it.

Another type of tolerance, called cross- tolerance, is also commonly spoken. In this one develops tolerance to a drug that at the same time extends to other similar substances. It tends to occur with substances that exert similar effects on the brain.

Conversely, reverse tolerance is a state in which greater or equal effects occur with a lower dose of the substance. It is very typical in chronic alcoholics. In some of these cases, they can get drunk with only a couple of drinks.

Can tolerance be reversed?

The brain is plastic. If you stay for long periods of time without using drugs, you will again adapt your receptors and neurons to the new situation.

Also keep in mind that most drugs or substances have more of an effect. Thus, tolerance tends to develop differently for each of them.

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For example, heroin produces a very quick tolerance for the effects of euphoria and well-being. Despite this, the effect of respiratory depression (reduction in breathing rate) remains unchanged. Therefore, it is possible to be overdose or death.

Decreased tolerance depends on the history of substance abuse. That is, if the drug has been taken in long periods before abstinence, it will take longer until the brain structures return to their initial state.

However, in cases of chronic drug abuse, the level of harm to the organism may be permanent, even if the substances are abandoned.

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