Addiction generally develops when someone uses a substance which signals the release of mood-altering chemicals in the brain (e.g., epinephrine, norepinephrine, dopamine, saratonin), which is the "good" part of the intoxication/high. However, our brains are only wired to process so much of these chemicals on a daily basis, and when the brain becomes flooded with these chemicals, it creates new receptors to tolerate the overload. As a result, a person experiences tolerance, which means they now need a larger dose of the substance to achieve the same "good" feeling as before. In doing so, they continue to flood the brain. This develops a biological dependency now in the brain for these chemicals in order for the brain to continue to send messages correctly to the rest of the body including major organs like the heart, lungs, and kidneys. When the brain is deprived of the levels it now craves, people experience withdrawal symptoms which vary depending on their drug of choice.
People can acquire an addiction to many types of mood-altering substances (e.g., alcohol, drugs, caffeine, sugar) and even process addictions for certain activities (e.g., shopping, gambling, video gaming, sex/pornography). Addiction is a dependence on that mood-altering substance or activity to feel "normal" physically and emotionally.
People use mood-altering substances for a variety of reasons (e.g., social/cultural factors, immaturity, curiosity, expectations of self and/or others). It is developmentally appropriate to be curious about new experiences (including alcohol and other drugs), but abuse occurs when there are negative consequences from use. Often, people overlook the negative consequences in order to enjoy the "benefits" of the substance, increasing their risk of further abuse and eventual addiction/dependency.
Addictions can develop at any time along the lifespan. There is an increase of incidence during ages 13-26 due to environmental factors (e.g., availability of various substances, decreased supervision/accountability, social pressures/expectations, experimental attitudes) which are all developmentally appropriate. Another factor to consider is that the human brain does not finish developing until age 25; the last part of the brain to develop is the frontal lobe, which governs executive functioning (e.g., judgement and problem-solving).
The role of drug use for college age students varies depending on the person and their lifestyle. Young adults (ages 18-25) who attend college associate with new peers who may have varying expectations and tolerances for alcohol and other drugs. As a result, students are prone to binge drinking (i.e., drinking to intoxication irregularly) and negative consequences (e.g., DUI, alcohol poisoning, fights, reckless behavior, severe hangovers). They may also experiment with a wider range of substances than previously, in larger quantities than normal, and experience negative consequences (e.g., overdose, bad trips, reckless behavior, or harmful side effects). This impacts their ability to maintain class attendance, engagement, participation in sports and other extracurricular, employment, and stable/healthy relationships. Combining this stress with the normal stresses of the college experience can be catastrophic, leading to other problems (e.g., mental health symptoms, financial or legal difficulties, academic problems).
There is an old assessment tool for substance abuse that I like: CAGE. If you have tried to C-Cut back and have found it was difficult, If you have noticed other people are A-Annoyed with your use and complain about it, if you feel G-Guilty about your use like you lie about it or hide it from others, or if you notice that you need it to feel normal as an E-Eyeopener for your day. If the answer to any of these is "yes", then you may want to talk to someone (see below). Other warning signs include the presence of negative consequences from use. If you notice people are ending friendships/relationships, losing jobs, getting in trouble at school, experiencing health problems, hygiene gets worse, feeling depressed/anxious, etc.
There are many things people can do to reduce their risk of negative consequences from involvement with alcohol and other drugs:
Keep it legal - Avoid illegal use of substances to prevent legal problems. Those laws came from somewhere, usually research that identified when use becomes dangerous.
Moderate use - Have a limit to how much of a substance you can use before it begins to have negative consequences for you. Most people metabolize alcohol at a rate of 1 drink per hour. There are apps you can use to calculate your approximate BAC and track your drinks. You can also buy breathalyzers over the counter to better learn how BAC levels feel to you, which will differ from other people of other sexes, sizes, and tolerance levels.
Know what your using - Not all joints are filled the same. Just because a pill gives your friend a certain affect doesn't mean it will do the same for you. Accepting a free drink sounds awesome but it could be drugged.
Have a plan - If you know there is a chance of alcohol or other drug use, reduce your risk of negative consequences by eating food, drinking water, do not use alone, do not drive, etc.
Ultimately, the substance is not the problem. It is what we do with the substance(s) that create problems for ourselves and/or others. For example, if you drink too much water, it will deprive your brain of the sodium it needs and you will slip into a coma. Anything can be abused. You have to know yourself (i.e., your needs and limits) to prevent abuse which may lead to addiction. College students and other young adults are still figuring themselves out and testing the limits, which puts them at risk for all kinds of risky behavior and negative consequences. Some great resources about substance use, abuse, and dependency are:
If someone feels that their substance involvement may be a problem because its causing problems, they should talk to someone they trust (i.e., someone who would tell them the hard truth). They can also attend a local AA/NA meeting (https://www.aa.org/pages/en_US/find-local-aa) and discuss their concerns with the leader of the meeting. Most colleges have a counseling center with free or reduced rates for students where you can discuss these issues. If that is not available, people can discuss this with their primary care physician as well. And of course, a trained counselor.