22 Feb Why Are Some Drugs More Addictive than Others?
According to the National Institute on Drug Abuse (NIDA), addiction “is considered a brain disease because drugs change the brain; they change its structure and how it works.” Drugs do this by interfering with the brain’s natural communication system, which is composed of neurons (nerve cells) that communicate through messages carried by chemicals called neurotransmitters. To some extent, the impact on the brain is similar for all addictive drugs: drugs produce a feeling of euphoria by overstimulating the brain’s reward system through a flood of the neurotransmitter dopamine. However, not all drugs do this in exactly the same way, which is why some drugs are more addictive than others. The addictiveness of a drug depends on a variety of factors, including its mechanism of action in the brain, how quickly it arrives in the brain, and the severity of withdrawal symptoms when the drug is stopped.
How Drugs Affect The Brain
To understand the differences in the ways different drugs affect the brain, we must first have a basic understanding of how the brain communicates. In order for a neuron to transmit a message to another neuron, it releases a chemical neurotransmitter. This neurotransmitter travels to the receiving neuron, where it attaches to a site called a receptor. If the receptor believes the neurotransmitter is valid, it will forward its message on. The neurotransmitter is then recalled to the neuron that released it via the transporters on that cell, which shuts off the signal between the neurons.
Because drugs are also chemicals, like neurotransmitters, they can interfere with this natural system of communication. Drugs like marijuana and heroin mimic the chemical structure of neurotransmitters, tricking receptors into activating and transmitting messages. Although they have similarities to natural neurotransmitters, these drugs affect neurons differently and result in the transmission of abnormal messages. Other drugs cause neurons to release much larger amount of neurotransmitters than usual, or prevent the transporters from recycling neurotransmitters. This is the way drugs like amphetamine and cocaine work.
Eventually, if drugs are taken multiple times, the brain will react to this unnatural increase in dopamine and other neurotransmitters by producing less dopamine or reducing the number of available receptors. Without the drug, the user’s dopamine level becomes abnormally low, meaning they need to take the drug just to return their dopamine level to normal—and they need to take even more of the drug in order to get the same high. The structure of the brain may also change, affecting behaviors such as self-control and decision-making. These changes have been shown in brain imagining studies of addicted individuals, and may play a significant role in addiction. Methamphetamine abuse in particular has been shown to result in long-lasting—sometimes permanent—changes in the brain.
How Quickly Drugs Work
The faster a drug reaches the brain, the more addictive it is likely to be. Some drugs affect the brain within seconds of administration, resulting in an intense response that quickly fades. This sudden euphoria, replaced quickly by more normal feelings, often leads drug users to take more of the drug.
Drugs that are smoked or injected into a vein reach the brain very quickly and result in an intense but short-lasting high. These drugs are highly addictive and include methamphetamine, cocaine, crack, and heroin.
Severity of Withdrawal Symptoms
Some drugs are particularly addictive because they result in severe withdrawal symptoms if stopped. As discussed above, prolonged use of a drug can lead to tolerance, or a lessening of the drug’s effects due to changes in the brain. Tolerance is a sign of physical dependency on a drug, meaning that withdrawal symptoms will be experienced if the drug use is discontinued. It is important to note that physical dependency and addiction are not the same thing; addiction has a psychological component that results in a compulsion to use a drug even in the absence of withdrawal symptoms. However, drugs that result in severe withdrawal symptoms can be among the most addictive, as the unpleasant symptoms of withdrawal encourage continued use.
For drugs that quickly leave the bloodstream, like cocaine, withdrawal symptoms can appear within hours. These symptoms often include depression, anxiety, and a craving for the drug. If these feelings are strong enough, they can drive a person to continue using the drug despite significant adverse consequences—the definition of addiction.
As you can see, there are a number of factors that determine the addictive potential of drugs. Some of the most addictive drugs are tobacco/nicotine, heroin, crack, cocaine, methamphetamine, crystal meth, caffeine, and benzodiazepines—all of which are either smoked, injected intravenously, have severe withdrawal symptoms, and/or result in a quickly-developed tolerance.
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