Addiction is the dark side of your brain’s capacity to learn and adapt. In essence, addiction is the result of your brain’s attempt to continue to function normally in an abnormal chemical environment.
Addiction differs from most other neurological conditions in one specific respect. You don’t have to do anything to get Multiple Sclerosis or Schizophrenia, but you do have to actively put the addictive substance into your body, and do so repeatedly, in order to trigger the maladaptive responses that cause addiction. In this respect, addiction can be seen as a self-inflicted wound, something that is the addict’s fault because it results from their poor decisions. However, similar assessments of blame could be applied to many other medical conditions. For example, in order to contract chronic Lyme disease, a person must choose live in or visit a part of the country where Lyme disease carrying ticks are present. He or she must enter an area with long grass or bushes without wearing insect repellent, (or have a pet that goes into these kinds of areas), and then fail to remove ticks within 24 hours of attachment and to fail to seek medical attention promptly after the appearance of a rash or fever. Lyme disease can be completely avoided by staying out of the Northeastern United States or always checking for ticks after any possible exposure and quickly removing them. People do not however usually blame the person with Lyme disease for the prolonged pain, weakness, and fatigue that they suffer. We recognize that many people engage in the same behaviors without getting Lyme disease because most ticks do not carry Lyme disease and most people’s immune systems area able to fight off the disease if they are exposed. Someone with chronic Lyme disease as just thought of as being unlucky. Similarly, however, most people who experiment with recreational drugs do not become addicted. The vast majority of people who consume alcohol do not become alcoholics. Most people who try cigarettes, or marijuana, or even cocaine or heroin, will just stop using them after a while. Whether or not a drug user will become a drug addict is a matter of both the amount and frequency of drug use, and their body’s physiological responses to the drug. In short, it is a matter of both bad decisions and bad genetic luck.
Nearly all drugs that are abused stimulate your brain’s pleasure or reward centers, either directly or indirectly. (Alcohol works slightly differently as I will discuss later.) The purpose of these reward centers is to encourage you to repeat actions which the history of your species suggests are likely to help keep you alive or help you reproduce. Eating a good meal when you are hungry, slaking your thirst after a walk in the desert, winning a competition, or having sex all trigger your reward system. When your reward system is activated, it tends to lock in whatever behaviors preceded its activation. You have an impulse to repeat the actions that triggered your reward center whenever you find yourself in a similar situation. Drugs that activate your reward systems therefore tend to make you want take them again, especially when you are in similar situations or environments.
At the same time that you feel a desire to use the drug again however, the drug is causing problems for your brain. Addictive drugs over stimulate brain cells (neurons) in your pleasure or reward centers. The drugs are so much more potent than the natural brain chemicals (neurotransmitters) which they mimic that they can actually be toxic. When a neuron is stimulated enough to cause it to fire off a signal to other cells, one of the things that happens is that calcium is released from stores inside of the cell. If a neuron is stimulated way too much, so much calcium is released that the high calcium levels interfere with processes that are necessary to keep the cell alive. This causes something called excitotoxicity. In order to avoid being over stimulated to death, neurons will first try to make themselves deaf to the chemical signal by reducing the number of receptors that respond to the chemical. They will next tell nearby cells which make the neurotransmitters which the drugs mimic to stop making so much neurotransmitter. These adaptations turn down the volume of the reward system. With the natural reward system of your brain turned all the way down, you are not able to feel pleasure in response to any of the things that used to make you feel good. In fact, you feel pretty lousy, because all of the negative signals are still operating normally. On balance, even a few negative signals will add up to a negative experience if there aren’t any positive signals to counterbalance them. Since nobody likes to feel bad, you are likely repeat the last action that made you feel good. You take more of the drug. And then you increase the dosage because you are not getting the same response. Eventually the cells which respond to the drug start dying. The drug then no longer even makes you feel good. All that the drug can do now is make you feel a little less bad. You would think that that would be enough to make an addict stop using. However most addictive drugs also damage the parts of the brain which help you unlearn habits that are no longer working for you. If the quality of the food at your favorite restaurant declines, your normal response would be to stop going there. If a drug that used to get you high stops getting you high however, you are likely to continue chasing that high by taking more of the drug and taking it over and over again.
The brain damage from long term drug abuse is more or less permanent. The brain of an adult just does not produce many new neurons to replace those that are killed by the excitotoxicity. This brain damage is not a side effect of the drug. It is the main effect. The temporary pleasure was the side effect. The whole reason for plants to produce chemicals like nicotine, opium, or cocaine, is to try to kill the insects or herbivores that eat them, or at least to disable the animals enough that they get eaten by predators before they do too much dammage. When a toddler dies from swallowing cigarette butts or a heroin addict ODs, that is exactly what the tobacco plant or opium poppy was trying to accomplish. Most of these addictive chemicals are, in fact, natural pesticides. Plants make these chemical to try and protect themselves from insects and larger plant eaters (herbivores). The man-made “designer drugs” are more deliberately designed to produce the same damaging effects. A drug dealer wants his customers to keep coming back and giving him more and more of their money. If your customers are brain damaged in a way that makes them feel terrible when they are not using your drugs, it is pretty good way to generate repeat business.
I mentioned earlier that alcohol acts slightly differently than most other addictive drugs. Alcohol generally slows down nerve conduction and reduces the ability of all of your neurons to send their messages. If a lot of the messages in your brain are bad news, then keeping some of those messages from getting through is sort of like feeling good. Alcohol tends to numb you to both pleasure and pain, but if there is more pain than pleasure in your life, then numbness is an improvement. Because people suffering from depression or post-traumatic stress disorder (PTSD) are feeling a lot of emotional pain, they are much more likely to abuse alcohol, or other drugs, than the general population. As happens with the use of other drugs, the brain (and peripheral nervous system) of a habitual alcohol user tries to adapt to the situation and alter its functioning to restore a normal level of communication. For example, if someone have been drinking a lot, for a long time, the nerves carrying touch sensation will start sending their ordinary “I’m still here” signals at a much higher rate, just so that some of the signal gets through. If the person then stops drinking and tries to “dry out”, all of those extra signals get to your brain and make the person feel like something is crawling under their skin. That is what the DTs are. All of the previously blocked signals are now starting to get through and it takes a while for the body to dial back the signal and restore normal sensation. Like other addictive drugs, alcohol is also toxic to neurons. But alcohol is not as toxic as some of the other addictive drugs and alcohol toxicity is not specific for any type of neuron. Rather, alcohol tends to increase the rate of neuronal death that normally occurs with age. This increase in neuronal death rates means that heavy drinkers tend to develop age related conditions such as Parkinson’s disease or Alzheimer’s disease at much earlier ages than the general population.
In addition to addictive drugs, certain behaviors like gambling can also somewhat over stimulate the reward centers. These stimuli are not as potent as some of the more addictive drugs but they can still lock in bad habits. The down regulation of neurotransmitter receptors in the reward centers after the strong stimulation of a big gambling win can make ordinary life seem dull and joyless. For some people, activities like gambling can begin to feel like something that they need to do. Something that started out as harmless fun can become a compulsion.
Once drug use has crossed a threshold of causing neuronal death, the brain damage becomes irreversible. At early stages in drug use, your neurons can just go back to making more neurotransmitters and receptors. Cell death however is permanent. The adult brain makes very few new neurons. However, the brain does continue to be able to adapt. If you stop using drugs long enough, your brain tries to do a little rewiring in order to make the neurons that have survived work more efficiently. The craving for the drug may not ever go away completely, but it does tend to become weaker over time. Furthermore, if an addict really wants to stay clean, the compulsion to use the drug can be overridden by an even stronger compulsion not to use. Some addicts repeat their self-destructive patterns and go back to using the same or different drugs but many addicts do manage to stop using and stay clean and sober.
There is not a lot known about how to break a cycle of addiction. We do know that an addict first needs to rid his or her body of the drug long enough for his or her nervous system to begin to readapt to function without the drug being present. In cases of long term opioid abuse, maintenance doses of less addictive opioid drugs such as methadone, naloxone, or buprenorphine may alleviate persistent symptoms caused by loss of opioid producing neurons and reduce the risk that the person will return to drug use. We also know that it is very helpful for an addict to stay away from people and places that were associated with drug use. It is also a good idea for an addict to create new habits to replace the habit of using drugs. The patterns of behavior that were locked in by the brain’s reward system when an addict first started using are hard to erase. Avoiding the signals that could trigger an urge to repeat the old behaviors makes it easier to stay clean. Of course, all of this is much easier for someone who has the financial resources to change where they live. Many addicts however do not have this option. They cannot afford to move and must continue to live in the same neighborhoods, walking past the same bars where they used to get drunk every night or seeing the same dealers who used to supply them with their fixes. It requires a great deal of strength not to fall back into the old bad habits under such circumstances.