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Tolerance to Alcohol and Drugs

The body naturally develops tolerance to alcohol and other drugs. Different parts of the body develop tolerance in different ways. Tolerance that occurs in the brain is noticeable because people recognize when they feel less drunk or high than usual. Tolerance can be dangerous, though. When people increase the amount of the substances they consume, they risk damaging parts of the body that don’t develop tolerance.

Tolerance occurs when someone repeatedly uses alcohol or other drugs. Over time, the body no longer reacts to the substance the same way it did the first time the person consumed it. With increased tolerance, the brain may not feel euphoria or could experience coordination problems. The rest of the body may not suffer nausea or other side effects of substance abuse.

The level of tolerance and the length of time it takes for tolerance to develop depend on a number of factors. Genetics play a significant role in the way the body reacts to alcohol and other drugs. Some drugs cause tolerance more quickly than others. The environment in which a person consumes the substance also plays a large role in his or her level of intoxication.

The phenomenon forces those intent on achieving euphoria or intoxication to consume higher doses of the substances or to consume them in riskier ways. For example, a person who develops a high tolerance to alcohol after drinking beer over long periods of time may begin to drink shots of liquor in short periods of time to get drunk. A person who develops a high tolerance to heroin after smoking it may begin injecting it.

People may mix different types of drugs to achieve their desired side effects. These methods of administration drastically increase a person’s risk of negative side effects, such as blacking out, contracting diseases or overdosing.

Tolerance alone is not necessarily a health problem. Patients who take opioids, such as hydrocodone, for pain relief usually develop a tolerance to the drug and require increased doses to achieve the same effects. When their injury heals and they stop taking the drug, their tolerance decreases. The next time they have a surgery or an injury, the doctor can usually prescribe a low dose to achieve pain relief.

It can be dangerous, though. People in recovery from addiction are at a high risk for overdose if they relapse because their tolerance diminishes during detox. The body no longer reacts to the drug the same way it did before abstinence. When a person administers the dose that they were last used to, their risk of overdose is amplified.

Types of Drug Tolerance

Drug tolerance can be defined as diminished responsiveness to alcohol or another drug as a result of repeated consumption or administration. Tolerance can be achieved in different ways, and experts have discovered three types of tolerance: pharmacodynamic tolerance, metabolic tolerance and tachyphylaxis.

Pharmacodynamic Tolerance

Feelings of intoxication are a result of a drug’s interaction with nerve receptors in the brain. Pharmacodynamic tolerance is a result of a drug’s repeated interaction with nerve receptors. The brain becomes used to the presence of the drug and requires higher doses to feel the effect previously achieved by lower doses. Opioids cause pharmacodynamic tolerance.

Metabolic Tolerance

Metabolic tolerance occurs when the body metabolizes drugs at an accelerated rate. Unlike pharmacodynamic tolerance, the drug still affects the brain the same way. However, the body metabolizes — gets rid of — the drug more quickly. Thus, the same drug has a diminished effect.

Metabolic tolerance occurs when alcohol or other drugs cause metabolic enzymes to synthesize. Chronic alcohol consumption activates liver enzymes that contribute to metabolic tolerance.

Tachyphylaxis

Tachyphylaxis is a type of tolerance that occurs quickly after repeated drug use. Pharmacodynamic and metabolic tolerance usually take days or weeks to occur. Tachyphylaxis can occur within hours of administration or consumption.

Addiction to hallucinogens, such as LSD and DMT, is rare because they cause tachyphylaxis. However, the drugs aren’t harmless. People who use these drugs repeatedly sometimes need higher doses to achieve the same effects. Hallucinogens can cause long-lasting side effects, such as hallucinations and paranoia.

High Tolerance vs. Addiction

Addiction is a chronic brain disease that causes compulsive behavior despite negative consequences. Tolerance is a decreased reaction to substances of abuse. The two terms are often associated with one another, but they are not the same.

It is possible for someone who has developed high tolerance to hallucinogens to quit using them because they can no longer achieve the desired effects of the drugs. A person addicted to tobacco cannot quit smoking cigarettes as easily. He or she usually requires some type of assistance from friends, family or health care providers.

Tolerance is one of the most common precursors and side effects of addiction. It’s also a common precursor and side effect of dependence.

Dependence

Dependence is often confused with addiction and tolerance. Unlike addiction, dependence is not associated with compulsive, destructive behavior. A person dependent on wine may require a glass with dinner every night to avoid headaches, but they do not necessarily seek wine compulsively or drink and drive.

Dependence occurs when the receptors in the brain become used to the presence of the drug and only operate normally when exposed to the substance. Without the substance, the brain reacts negatively in a process called withdrawal. Withdrawal symptoms may be minor or severe depending on the substance of abuse and the severity of the dependency.

Patients receiving aggressive treatment for cancer often become dependent on painkillers, meaning they experience headaches or other withdrawal symptoms without the drugs. These patients receive opioids to treat pain and often develop a high tolerance to them, requiring higher doses to experience pain relief. But they rarely become addicted.

Most patients dependent on painkillers don’t act compulsively or perform self-destructive acts. When the pain goes away and the doctor stops prescribing the drug, they do not seek it on the street. Dependency can lead to addiction, though. Patients with a genetic predisposition to addiction or a history of substance abuse can relapse after being exposed to drugs in clinical settings.

Tolerance to Alcohol

There are several types of tolerance to alcohol, and they develop in different ways. Levels of consumption, frequency of consumption, environmental cues and genetic predisposition all contribute to how tolerance is developed.

Functional Tolerance

Alcohol disrupts the brain’s ability to function, but the brain adapts to alcohol exposure over time to prevent future disruption. This adaptation is called functional tolerance.

When a person repeatedly consumes low levels of alcohol, environmental cues and learning processes can promote the development of functional tolerance. When a person repeatedly consumes high levels of alcohol, functional tolerance can be developed without environmental cues.

People who have developed high functional tolerances to alcohol exhibit few signs of intoxication, even when their blood alcohol concentrations are high. Individuals with extremely high tolerances may be able to drink levels that could be fatal to someone with a low tolerance.

Acute Tolerance

Functional tolerance takes time to develop, usually several days or weeks of repeated exposure to alcohol. However, acute tolerance can occur in a single drinking session.

Acute tolerance refers to a decreased level of impairment to alcohol later in a drinking session when compared to the level of impairment at the beginning of the session. For example, a person who consumes four alcoholic beverages may feel less impaired after his or her eighth drink, even if his or her BAC remains the same.

Acute tolerance does not affect all levels of intoxication, but it can affect a person’s feeling of intoxication. People may believe they’re “sobering up” even when they aren’t. Their judgement, coordination and motor skills may still be impaired because those are not affected by acute tolerance.

Environment-Dependent Tolerance

Environmental cues can accelerate a person’s tolerance to alcohol. Studies indicate rats develop tolerance to alcohol when they receive it in the same room, and humans have exhibited similar tolerances when repeatedly drinking in the same environment.

An experiment published in the Journal of Studies on Alcohol found social drinkers performed hand-eye coordination tasks more effectively when they drank in a bar rather than in an office.

Learned Tolerance

People can learn to perform tasks more effectively when under the influence of alcohol.

In an experiment published in the journal Pharmacology Biochemistry and Behavior, people who practiced hand-eye coordination tasks under the influence of alcohol were able to more successfully complete the tasks after being exposed to alcohol a second time than people who practiced the task while sober.

Other studies have found motivation and the anticipation of a reward can contribute to more rapid tolerance development. Studies also show that people who frequently drive the same route while under the influence can develop a tolerance to alcohol, but they instantly lose the tolerance when an unexpected situation or event occurs on that route.

What Is a High Tolerance?

Anyone who consumes drugs for recreational or medical purposes needs to be aware of tolerance. Health professionals closely monitor patients’ tolerances to medications to ensure escalating doses don’t cause unwanted side effects.

The brain develops a tolerance to certain medications, but other organs may not. When the risks outweigh the benefits, the person’s tolerance may be called “too high.” In health care, the highest dose of a drug that does not cause unacceptable side effects is called the maximum tolerated dose.

Developing a high tolerance to alcohol and recreational drugs also comes with risks. Some people may be willing to abuse illicit drugs to achieve a high, but they may decide their tolerance is too high when they have to spend too much money on drugs to achieve the same high or when they begin to experience health-related side effects.

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

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:

Because drug and alcohol use affect multiple major organ systems, increasing dosage after developing a tolerance increases the possibility of health problems in all parts of the body.

A high tolerance also increases a person’s risk for dependence and addiction. Genetics, environmental factors and the substance of abuse affect a person’s likelihood of becoming dependent or addicted.

Some drugs are more likely to cause addiction than others, and some people are naturally more capable of resisting addiction than others. People surrounded by peers who abuse alcohol or other drugs are more likely than those with little exposure to alcohol or drug abuse to develop a substance use disorder.

A person who has developed a high tolerance to alcohol or other drugs should be aware of the dangers associated with heavy drinking or drug use. They should speak with their health care provider about abstaining from the substance. If they are dependent or addicted, they should seek treatment to assist with detox and to learn how to live without substances of abuse.

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