What Is Tolerance?

What is tolerance and how is it developed?

Tolerance to drugs and alcohol occurs when the body stops reacting to drugs or alcohol, after excessive long-term abuse Once the body has built up a tolerance to any of these substances, you will find that you need to increase the dose each time you use, to achieve the same high, you once did. If you continue using these substances to excess, you will require drugs or alcohol to function normally.

Physical vs Psychological Tolerance

Put simply, physical tolerance occurs when enzymes in the liver (responsible for metabolising toxins) become more active, therefore the metabolism of drugs and alcohol speeds up. This, in turn, causes a significant reduction in the number of cell receptors that the drug attaches to. For example, if you drink or use drugs regularly, your liver will boost the production of enzymes that break down alcohol, allowing your body to get rid of it quicker. Your body can also adapt to the regular presence of a substance by reducing the number of receptors they attach to. By doing this your body simply stops responding to what the drugs are telling them.

Behavioural tolerance is the psychological aspect of tolerance. Certain behaviours around drug and alcohol use can create habits in users. For example, you can become so accustomed to your drug-using environment that you’re not even aware of the effects of the drug. This type of tolerance also occurs if you’re told that a substance is/isn’t potent, and act accordingly, rather than by what you’re experiencing.

Tolerance vs Addiction

The words tolerance and addiction are often associated with each other; however, they are two very different phenomena. Addiction describes a chronic disease of the brain, which causes engagement in compulsive behaviours despite any negative consequences that could arise as a result.

Tolerance is characterised by a decreased reaction to substances of abuse and is a common precursor and side effect of addiction. It is important to remember that just because someone develops a tolerance to a substance, it does not necessarily mean that they are addicted to it. It only suggests that their current dose is not having the desired effect. Someone who has developed a tolerance can quit using at this stage, whereas a person who is addicted to drugs or alcohol cannot stop taking them suddenly, and doing so can be extremely dangerous.

What is tolerance

Types of Tolerance

There are seven levels of tolerance to chemical substances: acute, behavioural, dispositional, inverse, pharmacodynamic, reverse and select.

Acute Tolerance

When someone develops a tolerance to the effects of drugs or alcohol during a single session, it is known as acute tolerance. They may appear to be more intoxicated in the early stages of the session than they are towards the end. This is because the brain and central nervous system activity to immediately diminish the effects of a given substance


The brain of an experienced drug and alcohol user can quickly adapt and allow the user to suddenly appear sober as a way of concealing the use of substances. Behavioural tolerance allows users to use part of the brain not affected by substances when presented with a threat or situation of stress.


In the cases of certain substances, the brain is unable to process them itself and relies on the interactions between neurotransmitters and receptors. However, chemicals from drugs and alcohol interfere with these processes and the brain is unable to respond. Dispositional tolerance occurs when the body adopts this task and significantly speeds up metabolism so that the substances are quickly circulated through the blood to the liver, for removal. This process reduces the effects of the drugs or alcohol meaning that a higher dose is needed.

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Inverse tolerance is rather challenging to understand as it has dual characteristics. Inverse tolerance effectively causes changes in the brain and central nervous system with the way that chemicals are processed, thus affecting the body’s ability to handle drugs or alcohol. Inverse tolerance can also cause severe withdrawal symptoms in the case of relapses during the recovery attempt.


Pharmacodynamic tolerance is the process by which the brain actively works to weaken the impact of a foreign substance. The brain adjusts nerve cells, transmission processes, reuptake, and receptor to become desensitized to the substance, effectively producing an antidote to the substance.


Reverse tolerance refers to your sensitivity to a particular drug. This occurs depending on your body’s ability to break down and process the drug. Reverse tolerance is usually common in chronic drinkers whose livers are no longer able to function normally. This means the alcohol stays in their bloodstream for much longer and in large concentrations, which explains the increased sensitivity to, in this case, alcohol.


This type of tolerance is not very well-understood but refers to some cases where the brain selectively weakens some of the side effects of a substance, but not others. For instance, some people may smoke cannabis for a long period without feeling the same euphoric effect, although other parts of the body, such as the lungs, throat, and cannabinoid receptors, are being affected.

Tolerance vs Dependence

Tolerance and dependence are two very closely related concepts, which is why they are often used interchangeably. Both these processes co-occur during the adjustment of the body to the regular presence of a foreign substance. Once the brain and central nervous system have built up a tolerance to drugs or alcohol, it may also require the substance to function normally; this is known as physical dependence.

Without the substance, the brain reacts negatively in a process called withdrawal. Withdrawal symptoms can be minor or severe depending on the substance of choice and the severity of the dependency. Tolerance can develop without dependence. For example, it’s possible to need a higher dose of drugs/alcohol without needing it to function normally. However, developing a tolerance to a substance increases your chances of developing a dependence at some stage.

The Dangers of Drug Tolerance

Tolerance to addictive substances typically means the consumption of higher doses to achieve the desired effects, the consequences of which can be devastating. One major risk involved with developing a tolerance is overdose, the chances of which increase after a period of abstinence. This occurs after the complete cessation of drugs or alcohol, which causes the body to begin flushing out toxins, this is what’s known as a detox. Returning to the same dose you were taking before your detox will now be far too high for your system to effectively process, which can lead to overdose, coma, or death.

Dangers of having a high tolerance to alcohol include an increased risk of:

  • Cancer
  • Sexual difficulties
  • Vision problems
  • Bone loss
  • High blood pressure

The risk is increased because several organs, bones, and other anatomical parts don’t tolerate alcohol the same way the brain does.

Dangers of having a high tolerance to illicit drugs include:

  • Changes in appearance
  • Mental health problems
  • Weight loss

Getting Help for Addiction

Tolerance usually indicates the presence of a physical dependence which could lead to addiction. If you’ve built up a tolerance to drugs or alcohol, it’s likely you’ll require a medically supervised detox. If you’re unsure of the next steps, our admissions team will be happy to take you through a free addiction assessment in order to better understand your particular needs and suggest the best course of treatment. In addition to detox, our London clinic also provides:

Addiction assessments

Outpatient addiction rehab and therapy

Residential rehab referrals

Online addiction therapy

Recovery yoga


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If you need treatment but can’t travel to our rehab in the South East, we also provide referrals to rehabs in other areas in the UK and Ireland. Alternatively, you may find our Telehealth services more convenient. Telehealth allows our clients to receive help and support for alcohol or drug addiction remotely on platforms such as Zoom, Skype, or Teams.

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