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You might have heard of drug tolerance, especially in relation to drug misuse and addiction. But what is drug tolerance and why do we build tolerance to drugs?
We’ll take a look at the facts…
What Is Drug Tolerance?
Tolerance refers to an individual’s lowered response to a drug, which occurs when the substance is repeatedly used and the body adapts to its continued presence.
In practical terms, this means that a substance has less effect over time and a person may need larger or more frequent doses to achieve the same effect. It can occur with alcohol and prohibited drugs used recreationally, but also with many prescription medications.
Tolerance is a normal biological response to repeated exposure to certain substances.
Why Do We Build Tolerance to Drugs?
There are three main biological and psychological causes of drug tolerance, which can also interact and work together to decrease the effectiveness of a drug or medication.
The Brain Adapts to Repeated Drug Use
Many drugs work by stimulating or blocking cell receptors. In the case of drugs used recreationally, these will often involve cells in the reward circuit of the brain, but others may also be involved depending on the substance.
Over time, the brain adapts by reducing the ability of cells to respond to the drug in various ways, causing changes at the molecular level. This is sometimes known as neuroadaptation. In some cases, the system may reduce the number of active receptors (a process known as receptor downregulation), or cells may become less sensitive to the drug (desensitisation).
Increasing tolerance may make medications less effective. In the case of recreational drugs and other drugs that tap into the reward circuits, it can also reduce the ‘high’ or pleasurable feelings associated with using the drug.
A knock-on effect is that these changes in brain chemistry can also lead to the user becoming less and less able to derive pleasure from other things they once enjoyed, like food, sex or social activities.
The Body Becomes More Efficient at Processing Drugs
Over time, the body also becomes better at breaking down and metabolising drugs that are constantly or frequently found in the system. This can reduce drug concentration in the bloodstream, with the practical effect of reducing the drug’s duration and intensity. In medical terms, this can lead to pharmacological tolerance and the need for higher doses.
This process is often known as metabolic tolerance and largely involves the production of certain enzymes that help the liver to break down active substances.
Behavioural Tolerance
Behavioural tolerance essentially involves the human ability to adapt and continue to function despite intoxication or impairment. Part of the reason for this is that the brain may learn, practise and carry out tasks while in an intoxicated state. Environmental cues and anticipation of taking the drug can also trigger a chemical response to maintain balance before the substance even enters the system.
Behavioural tolerance can include ‘masking’ the effects of a drug. For example, a cocaine user may learn to repress tics and give-away movements related to the stimulant. It should be remembered, though, that behavioural tolerance does not make activities like driving under the influence of drugs safer.
Does Tolerance Develop to Every Drug?
Tolerance does not develop to every drug and medication. Many medications like blood pressure drugs and antibiotics are able to maintain their effectiveness over long periods without needing increases in dose. Antibiotic resistance is a separate issue, in which the bacteria themselves evolve new defences allowing them to survive the medications designed to kill them.
Tolerance can be an issue with most psychoactive substances, though. This refers to drugs that alter brain function and directly affect how the central nervous system operates. It includes many types of drugs, including alcohol, opioids, stimulants, depressants and hallucinogens. Tolerance can develop differently depending on the drug involved and factors relating to the individual using them.
Some specific effects of a given drug can also cause tolerance quickly, while others do not. Overdose risks may remain high despite the user having a perceived tolerance in some areas.
Is Drug Tolerance the Same as Addiction?
Drug tolerance is not the same as drug addiction, although tolerance and dependence can play a part in the complex overall picture of addiction.
When it comes to addiction vs. tolerance, there are some key differences:
Drug Tolerance
This involves physical and sometimes behavioural adaptations that work to reduce responses to the drug in a number of ways.
Drug dependence
The body adjusts its chemical balance to adapt to the presence of the drug. Eventually, it can require the drug to function normally, with a range of withdrawal symptoms occurring when it is reduced or removed.
Addiction
Addiction involves a loss of control and compulsive substance use or behaviours despite harmful consequences. People who are addicted to drugs will continue to use them despite negative impacts.
Why Is Increasing Tolerance Dangerous?
Increasing tolerance can often lead users to take larger doses or use substances more frequently. This can be harmful whether drugs are used recreationally or users are seeking the beneficial effects of drugs such as painkillers that are no longer as effective. Some people may be tempted to mix different drugs or try other substances to chase their initial high.
Taking larger amounts of some drugs can increase the risk of overdose and other issues such as slowed breathing for opioids and cardiovascular damage for stimulants, even if the noticeable effects are less apparent.
Heavier continued use can also affect finances, relationships, work and other aspects of life, as well as increasing the risks of addiction.
Can Drug Tolerance Be Reversed?
Tolerance often decreases after stopping drug use, but this can depend on the substance involved.
It’s worth noting that returning to previous doses after abstinence can significantly increase overdose risk and that detoxification is always safer when undertaken under medical supervision.
Drug tolerance is a biological adaptation rather than a personal failing and occurs in medical settings as well as in relation to recreational drug use. It can increase the risks of drug misuse, though, and should always be taken seriously.
If you are concerned about your own or someone else’s substance use, you should seek professional advice as soon as possible. Get in touch with Rehab Clinics Group today for confidential information and support.
