What is drug tolerance?

Basil Manning
What is drug tolerance?

In the field of drugs there are many concepts that should be known. One of them is tolerance. However… What exactly is tolerance and how is it related to addiction or other concepts, such as the margin of safety or the active dose? Today, we explain it to you


  • What is drug tolerance?
  • Tolerance types, safety margin and active dose
    • Cross tolerance
    • Reverse tolerance
    • What is the margin of safety?
    • What do we understand by active dose?
  • Drugs that cause tolerance
  • Difference between tolerance and dependence

What is drug tolerance?

The concept of tolerance in the field of drugs occurs when a person consumes them continuously. This makes the body take on this substance, so that the effects it produces on it are not so clearly perceived..

However, this substance is equally toxic to the body. That is to say, the fact of developing tolerance to a specific drug does not reduce the harmful effect that it produces inside our body..

Rather, the opposite happens: the body will end up needing to consume a greater amount of this drug to achieve the same effect that it previously achieved with a lower dose. This is a clear sign that you are beginning to be addicted to it.

In this way, they will end up developing a dependency that will increase as the person becomes better tolerant of the drug in question, since each time they will need a higher dose to obtain the same effects..

This occurs because the receptors in the brain are no longer sensitive to the addictive substance. This makes the drug user need to consume a greater quantity to be able to perceive the effects again..

Tolerance types, safety margin and active dose

Within tolerance, experts differentiate two types.

Cross tolerance

The first of these is cross tolerance, which takes place when a person develops tolerance for a type of substance and this is extended to all similar substances.

Reverse tolerance

On the other hand, there is what is known as reverse tolerance. That is, when with a lower dose we achieve the same effect. This is usually used in cases in which a dependency is being fought: this method is used to, little by little, leave behind the addiction to it and lower the tolerance level.

What is the margin of safety?

The safety margin refers to the term Therapeutic Index (TI), which is the relationship between the dose in which a certain drug or drug is capable of causing death (lethal dose) or an adverse effect, and the dose of the same that causes the desired therapeutic effect (effective dose). Thus, the difference between the effective dose and the dose that causes serious harmful reactions or risk of death is known as the safety margin..

What do we understand by active dose?

It is the dose in which a drug or drug has an effect on the body. This dose varies according to the weight and complexion of the person, since there may be important differences in absorption. A dose of a drug for a child weighing 20 kilos will not be the same as for a man weighing 80 kilos.

Drugs that cause tolerance

When we talk about drugs we mean a wide spectrum of substances, both legal and illegal. Although we normally assume that the latter are the most dangerous and, furthermore, to which we attribute the concept of drugs as such..

However, there are many drugs that are legal and that, in the same way, produce a harmful effect on the body that can be lethal. One of them is alcohol, a substance that has social approval and that we are used to consuming on a regular basis..

This is one of the factors that makes it even easier to slip into dependency and develop a tolerance for it. The same thing happens with other types of drugs such as tobacco, or one of the lesser known: caffeine.

Many people do not know that caffeine, although legal, is still a drug to the extent that it affects the behavior of those who consume it and generates dependence. As with those mentioned above, this produces a tolerance that causes the person to need to increase the doses to obtain the same effect..

Difference between tolerance and dependence

Although closely related, there are fundamental differences between the concepts of tolerance and dependence. While it is true that due to tolerance we can detect that a dependency is developing.

The latter takes place when the individual who consumes a drug continuously feels that he cannot lead a normal life without taking his dose of it. In this way, the consumption of this drug ends up conditioning their day-to-day life and affecting aspects of their personal and professional life..

Tolerance is therefore a sign that we must pay special attention to when we identify it. This can indicate that we are beginning to be addicted to a substance, both legal and illegal, and therefore, we can develop a physical and emotional dependence towards it that ends up interfering in our daily lives.

Developing tolerance to a drug is also very dangerous for another no less important reason, and that is that by needing to consume higher doses of a toxic substance, we will be producing much greater damage in our body.

Thus, it is convenient to know that dependence can develop towards illegal drugs such as hashish or cocaine, but also even others that are legal, such as drugs, alcohol, tobacco or caffeine.

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