How do drugs affect the nervous system?

The use and abuse of drugs is a serious social and health problem on a global scale. Substance abuse kills, directly or indirectly, about 11.8 million people annually.

Alcohol and nicotine take the dubious prize when it comes to lethality: for them, 11.4 million people die earlier than expected each year. According to the WHO, up to half of the people who use tobacco end up dying thanks to it.

The prevalence of substance use disorders is estimated at 1.5% of the world's population, although in some disadvantaged regions this percentage rises to 5%. As low as these data may seem, do not be fooled: one in 5 people in the world (20%) uses tobacco. The fact that addictive behavior is not reflected in epidemiological data depends solely on whether the person is lucky in not paying for this dependence at a physiological level.

With all statistics we only want to make it clear that the consumption of addictive substances is charged as many lives and causes as many pathologies as many pandemic events caused by viruses and bacteria With the intention of taking a more biological and anatomical approach to this global problem, here we will review the subject of

how drugs affect the nervous system.

• Related article: "Types of drugs: know their characteristics and effects"

The bases of drugs

The World Health Organization (WHO) defines a "drug" as any therapeutic substance or not that, introduced into the body by any means of administration, produces an alteration, in some way, of the natural functioning of the individual's central nervous system and is, in addition, capable of creating dependence. It should be noted that the dependence developed can be physiological, psychological or both.

The American Psychological Association (APA) recognizes several types of drugs in use, grouped into 10 categories different: alcohol, caffeine, cannabis, hallucinogens, inhalants, opioids, sedatives, hypnotics (including anxiolytics), stimulants (cocaine and others) and tobacco. These are the substances that are considered addictive today, but surely not the only ones.

Among the activities that can generate dependency, currently only one is considered potentially pathological: gambling. Surprisingly enough, the altered reward circuit in a gambling patient has been shown to responds similarly to the stimulus (winning a prize money) that a cocaine addict upon receiving a new dose. Other activities that could share mechanisms with drugs, such as video games, compulsive shopping and chronic exercise, are still being evaluated.

• You may be interested in: "Parts of the human brain (and functions)"

Drugs and their effect on the nervous system of the human body

Let's start with the basics: nicotine. When a person smokes a cigarette, the nicotine passes into the bloodstream, then into the brain and only in 7 seconds produces the excitation in part of the neurons located in the ventral tegmental area (VTA), which send the signals to the nucleus accumbens. The latter is responsible for producing dopamine, the neurotransmitter and hormone that make us feel that "rush" or shock of well-being.

In the case of tobacco, this sensation is very ephemeral, because as soon as the nicotine acts, it stops doing so: the physiological peak of this drug is 7 seconds and its range of descent another 7. What's more, the more the neurons and circuits of the nucleus accumbens are exposed to the substance, the more of it will be required to elicit the desired response. This creates tolerance and long-term dependency.

To find out how drugs affect the nervous system, we can turn to another much more aggressive: heroin. This drug quickly enters the brain, attaches to opioid receptors in cells located in different areas and causes changes in the excitability of neurons, stimulating the presynaptic release of gamma-aminobutyric acid (GABA), among others things.

When it comes into contact with this drug at the nervous level, it produces a generalized sedative effect and a well-being indescribable (the level of dopamine in the described reward system is increased by 200% in models experimental). All this causes euphoria, drowsiness, a sensation of heat and a gradual loss of consciousness, accompanied by a powerful analgesic effect. People who have consumed it do not lie when claim to be "in a cloud" in the moments after the injection.

Finally, we can dissect the nervous effects of cocaine, the third of the drugs most present in the general culture. Once consumed, the effects at the central nervous system level are noticeable in a matter of 10 seconds (inhaled) and 3-5 minutes, if it is consumed intranasally. This compound inhibits the action of monoamine transporters, resulting in vasoconstriction in the blood system, elevated blood pressure, tachycardia and increased cardiac output. All this reports a very characteristic feeling of activation and euphoria.

Chronic cocaine abuse puts the patient at risk for many events, such as having a stroke (cerebrovascular accident), subarachnoid hemorrhages, intraparenchymal hemorrhages and many other things more. In general, every drug addict is seven times more likely to suffer an ischemic heart attack, a value that is multiplied even more in those who use cocaine.

Beyond all these mechanisms, it should be noted that dependence alone also modifies the functioning of the patient's nervous system. When withdrawal syndrome occurs (72 hours after completely cutting off the use of a substance), the person experiences anxiety, restlessness, difficulty concentrating, nervousness, stress and other associated sensations. The addict's brain can only function "normally" in the presence of the chemicals described. When they are removed, the nervous system fails.

Resume

As you have seen, the drugs function similar to that of the neurotransmitters circulating in the human body: reach an area, stimulate or inhibit cell activity and generate a short-term response. When its peak of activity ceases, the individual physiological state returns to normal, but as dependence is generated, reaching this "normality" is increasingly complex.

In addition, you must bear in mind that we have moved on purely physiological grounds. Addiction to a substance can also have psychological bases and, therefore, there are people who can manifest addictive mechanisms towards substances that the body does not really need at the time of crisis. Undoubtedly, we still have a lot to investigate as a society to elucidate the mechanisms of dependency in the human mind.