Addiction Medicine Made Easy | Fighting back against addiction

The Brain Science Behind Addiction

• Casey Grover, MD, FACEP, FASAM

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Your brain is ancient, but your world is not. We unpack how a hunter-gatherer reward system runs into modern dopamine superstimuli—engineered foods, infinite feeds, one-click buys, and potent drugs—and why that mismatch can spiral into addiction. Using clear language and vivid examples, we explain cravings, compulsion, and consequences through the lens of dopamine: how normal rewards help us survive, how substances hijack that circuitry, and how constant notifications keep the throttle stuck open.

We go deeper into the factors that raise or lower risk. Genetics account for roughly half of vulnerability and often determine a “drug of choice,” where one person feels sick from alcohol while another feels energized and social. Then we connect the dots between mental health and substance use. Depression, anxiety, ADHD, and PTSD frequently overlap with addiction, and treating one without the other rarely works. The ACEs research shows how chronic childhood stress reshapes the brain and the body, setting the stage for later disease. PTSD flips fight-or-flight on at the wrong time, and many people reach for alcohol or cannabis to blunt nightmares and panic, only to worsen the cycle.

Timing is pivotal. Teen brains run on lower baseline dopamine yet respond fiercely to novelty, making early use more rewarding and more dangerous. We share practical insights about delaying use, protecting brain development, and building real skills for stress, sleep, and conflict. A candid case study ties it together: a young adult mixing alcohol and cocaine, a missed PTSD diagnosis, and a turning point when care shifts to trauma therapy and targeted medications. The takeaway is hopeful and clear—when we treat the pain beneath the substance and rebuild healthy rewards, recovery becomes possible and durable.

If this conversation helped you see addiction more clearly, subscribe, share the episode with someone who needs it, and leave a review with your biggest takeaway. Your support helps more people find science-based care and hope.

To contact Dr. Grover: ammadeeasy@fastmail.com

SPEAKER_00:

Welcome to the Addiction Medicine Made Easy Podcast. Hey there, I'm Dr. Casey Grover, an addiction medicine doctor based on California's Central Coast. For 14 years, I worked in the emergency department, seeing countless patients struggling with addiction. Now I'm on the other side of the fight, helping people rebuild their lives when drugs and alcohol take control. Thanks for tuning in. Let's get started. Today's episode is on the brain science behind addiction. My daughter's school asked me to speak to the students about this topic, and I actually had the privilege of speaking to my daughter's class with my daughter Kai in attendance. The reason I mention her is when I asked the group questions, I had to make sure she didn't answer because she knows all the answers. She helped my wife and colleague Dr. Reb Close and I study for our addiction medicine board exam. So I gave this lecture on the brain science behind addiction to high school students, and I recorded it to share with all of you. One quick clarification. And to keep the kids interested, I brought quite a few of them to the presentation and tossed them into the audience. I hope you find this topic helpful. And with that, here we go. So today we're going to talk about the brain science behind addiction. And to start off, does anyone want to give me a definition of what addiction is? I know Kaino's because she helped me pass my board. 100%. That's as simple as it is. You like something, it hurts you, and you can't stop. Okay, so there's an official definition. So as doctors, we have professional societies, and we have one called the American Society of Addiction Medicine. And this is the definition that they give. I don't necessarily know if it's helpful to read it, except that it is a treatable condition and it is a chronic medical condition. So once it develops, it's like asthma. You have it, it has to be managed. And the simplest way to think about addiction is there are three things that happen. You do something, whether it's gambling, whether it's looking at pornography, whether it's cannabis, whether it's alcohol, whatever it is, you do it. You have cravings to do it, meaning you have this intense desire to do it. You do it compulsively, meaning you can't control it. And then you have consequences. So one of my patients right now is in jail because she relapsed. One of my patients I saw yesterday will face two years in prison if he uses any drugs or alcohol. One of my patients just lost custody of two of her kids because of her addiction. So that's the consequences. So that's really what addiction is. Okay. Now we are going to talk about the why, why this happens. Does anyone know what dopamine is? And I know Kai knows because she helped me pass my boards. So I'm going to give my daughter a high five. That is dopamine. We're going to talk exactly why we have it and what it does, but we will come back to dopamine multiple times as we talk about this. Okay. So just a level set, dopamine is the chemical in our brain that makes us feel good. Now, how long do you think we as human beings it takes for us to meaningfully change in response to our environment? So, in other words, how long does it take for us to evolve? Any guesses? 21 years. I need it's much higher. Go ahead. Any guesses? Yeah.

unknown:

Like a thousand.

SPEAKER_00:

Like a thousand years. Yeah. So probably it's somewhere between a thousand and five thousand years for us to actually meaningfully change. And the reason I bring this up is we are still wired to be hunter-gatherers. So our brains do not understand cars, social media, technology, addictive food, alcohol, cannabis. We're still wired to decide today who's going to go pick fruit and who's going to go hunt deer. So we will talk about that hunter-gatherer brain, but that's actually how we're wired. Now, as hunter-gatherers, our first issue was we had to not die. Forgive me for being blunt. We are not apex predators. So right now, if a mountain lion came in and chased one of us and got one of us, that would be the end of our life. Or if we are a small tribe and there was a neighboring tribe that was hostile, they might come attack us. So we are wired, number one, to look around and say, Am I safe? Is anything gonna hurt me? We'll talk about the brain chemistry of that in just a sec. Once we look around and we realize we're not gonna die, then we are our brain shifts and it starts focusing on how do we live as long as we can. So I apologize for the really bad graphics. I'm old and boring. I use ChatGPT to make images because I couldn't find anything on Google. So I said a man being chased by a bear, and this is what ChatGPT gave us. Okay, so the way the brain chemistry works is when we are in danger, we get a stress response. So people talk about like really liking adrenaline. That is what adrenaline is there to do. If you are in danger, your brain makes all these stress chemicals so you can run faster, be stronger, and fight back. Now, we'll talk about what that's like in the modern world, but that's what we're meant to have in this hunter-gatherer brain that we have. Okay. The next thing is once we are safe, our brain looks around and says, What do I need to survive? And there are three basic things. Okay. We need human connection because we have to have a tribe to protect ourselves. We have to eat. Why does food taste good? Dopamine. And we need to make more humans. We have to have babies. And obviously, the act that makes a baby is pleasurable, and that's what gives us the dopamine. Okay? So now in 2025, our brains are wired like hunter-gatherers, and yet we have Snapchat and electric cars and all sorts of stuff that our brain just doesn't know what to do with. So we are not in danger anymore of being eaten by whatever predator or being attacked by other neighboring tribes. So essentially, that turns into anxiety. We are looking for threat. We are afraid of something happening, and yet our brain doesn't understand that we're not in danger the way we used to be. So what's actually interesting is anxiety can be viewed as protective, right? If we were hunter-gatherers 5,000 years ago and one of you is really anxious, looking for something to hurt us, and I'm off picking daffodils, and a bear comes in, who's bear food first? Right? So we're actually wired to look for danger. And in this modern world, it feels really weird because worrying about Facebook likes isn't actually putting us in danger. So it's almost there's a mismatch between our world and how our brain works. Now, the one we're going to talk about today is the dopamine system. Okay. So again, we are wired for food, intimacy, and positive human connection. And that also really looks different. Okay. We've discovered all sorts of things that give us more dopamine than we were ever meant to naturally happen. I have a whole lecture on addictive foods and how the industry has made food really addictive. But this is an example of something that makes a lot of dopamine. This is a Reese's peanut butter cup. Do they grow on trees? No. It's engineered to have as much salt, fat, and sugar as our brains can tolerate to release the maximum amount of dopamine. Does anyone need any dopamine? I got a couple. Here we go. So literally, as you eat these, as you eat these, your brain is releasing more dopamine than blueberries in the back. Here we go, up in front. Right here. I got one more. Way in the back. Yes. Right there. So as you eat your Reese's peanut butter cup, I guess I should bring more next time. That is not how food is meant to taste for our hunter-gatherer brains, right? We are meant to eat basically raw fruits and vegetables, nuts and meat. And so the industry has figured out how to make us do things because it uses our dopamine system against us. So let's take a look. So on a normal day, our brain makes dopamine throughout the day, right? If you get an A plus on a test and you feel good, that's dopamine. Okay. Normally it goes from about 40 nanograms per deciliter to 100 nanograms per deciliter in your brain. Don't worry about the numbers, but that's the reference. Okay, we mentioned food. Do cheeseburgers grow on trees? No, they are engineered to be addictive. Okay. So a cheeseburger releases one and a half times the normal maximum dopamine. Okay. Sex in 2025 is different, right? We have pornography, sex toys, people get all sorts of bodily surgeries. Like even sex itself in 2025 is more stimulating than it was for us as hunter-gatherers. So that now releases more dopamine than we used to get. Nicotine is an addictive chemical. Why is it addictive? Because it releases more dopamine than we were meant to have. Now, cocaine is interesting. Cocaine's an upper, it's a drug that people use when they want to be like up and party and stay up all night. The way it works is it takes the dopamine in your brain. And normally your brain makes dopamine, and then when it's done, it reabsorbs it. What cocaine does is it actually prevents your brain from reabsorbing the dopamine. So when you use it, you get this intense flood of dopamine, which is why it's really addictive. And methamphetamine, which is also an upper, does double duty. It causes the brain to release more dopamine than normal and it blocks the reuptake. So you get these incredibly high levels of dopamine. There is nothing else that I'm aware of on planet Earth that releases this much dopamine. How hard do you think it is to quit meth? It's one of the harder ones. Because what ends up happening is basically what happens is once you hammer on your dopamine system to release more and more and more, your brain runs out. And so my patients who use meth when they're off meth and they have no dopamine, they're bored, they're anxious, they're depressed, they're flat, they can't feel good. Like literally giving someone a high five or a hug or eating something when you're coming off of meth, none of it feels good because your brain is out of dopamine. Here's another thing, just looking at how much dopamine gets released. You can see that dotted line is just the kind of the maximum normal dopamine that we release. Alcohol makes us release more nicotine, morphine, cocaine, amphetamine. This is why these substances feel good to the human brain and why we do more of them. Okay. Now there's one other thing that's interesting about dopamine in 2025 is that we are constantly stimulated for our brains to release more. Has anyone gotten a text message today? Has anyone be on social media today? Has anyone bought anything on Amazon this week? All of those things are unnatural to our brains and they release more dopamine. So what ends up happening is as hunter-gatherers, again, human connection, intimacy, and food, and then the rest of the day you were just cruising. Today it's like text message after DM, after Amazon purchase, after all this intense stimulation, our dopamine system is getting hit all day long. And we're in this chronic state of our dopamine system being overstimulated. So if you get really bored when your phone's not with you, that's what this is. Okay. This is if anyone likes to read or likes audiobooks, this is a book by a Stanford psychiatrist about all of this with our relationship to dopamine. And she called it a dopamine nation, meaning that as Americans, we are wired to constantly be looking for more dopamine. Okay. Now, the next question is we've talked about how the brain chemistry around that pleasure response, how that happens. Now let's talk about the genetic side of addiction. So I asked the question does addiction run in families? The answer is yes. Our estimates as doctors suggest that about half of our risk for addiction comes from our families. Why does that happen? Remember, I mentioned we'd be talking about dopamine a lot? Okay. My patients usually have a drug of choice. Okay. So some of my patients drink alcohol and they're like, that's the dumbest thing ever. It makes me nauseated and tired. Some people drink alcohol and they love it, and that's the genetic piece. Truly, some people drink a beer and their dopamine goes off the charts from alcohol. Some people drink a beer and they feel tired and sick to their stomach. And that is the genetic component. One of my patients, in regards to opioids, like fentanyl, she's really interesting. So I saw her three weeks ago, and she uses opioids to wake up, feel more productive. It helps her mood, it helps her anxiety. And you guys probably remember opioids are downers. They're supposed to do the opposite. And yet she literally is, oh my gosh, when I take fentanyl, I can clean my house and I can get my chores done. It's an opposite effect. So her brain genetically releases more dopamine when she gets an opioid. And she doesn't like alcohol. She doesn't have that genetic predisposition with alcohol. We had a family friend have surgery, and I got a text message of oxycodone is stupid. I'm tired and I feel really unsmart. That person does not have that genetic predisposition to releasing a lot of dopamine with opioids, which is great because she's really not likely to be addicted to it. So it is a very reasonable question for you as young adults to ask your family: does addiction run in our family? And if so, to what substances? You all will go off to college and there's alcohol and drugs everywhere in college. That's actually what I talk about the seniors with. And yeah, it's reasonable to know how your family responds when people use drugs and alcohol. Okay. The next question is how does our lived experience affect addiction? Okay, and there's a couple of parts to this. The first is we're gonna talk about, and this gets really dark, traumatic experiences. We're also gonna talk about mental illness and how they intersect. Okay. So in my world as a doctor, there's what's called dual diagnosis, which is basically where a person has a mental illness and an addiction. And as a doctor, I cannot successfully treat either one unless I treat both. Let's imagine you're depressed and you drink alcohol to feel better. I have to treat both. I have to get you off of alcohol and treat your depression. So you guys all remember from math a Venn diagram of what overlaps. And you can see in this graphic, the overlap between addiction and mental health is pretty small. Okay. And given what I do professionally, this is incorrect. And it actually looks a lot more like that. Meaning, almost all of my patients have addiction and a mental health condition. Okay. I have maybe, let me think, I think I maybe have four or five patients who are the exception and do not have a mental health condition and addiction. And a lot of what addiction is, is like people don't like how they feel and they use a substance and they temporarily feel better. And so they do it again, not realizing that the substance harms them in the long term. This gets really dark, and I apologize. So we're going to talk about adverse childhood experiences, which is abbreviated as ACE, and we call them ACE, thus, the ACE on the slide deck. So you guys heard of Kaiser Permanente? Yeah, it's a big hospital system. They literally have millions of patients, and they have the data to be able to find out like big trends in people's health by say, we're going to look at two million people and see what factors are associated with them developing diabetes. So Kaiser asked years ago, why do people get sick? Why do they get diabetes? Why do they get heart disease? Why do they get depression? Why do they develop addiction? And they found reliably that difficult circumstances in a person's childhood leads them to develop these illnesses as adults. So here are what are commonly thought of as adverse childhood experiences. So getting physically abused, emotionally abused, or sexually abused as a child, being physically or emotionally neglected as a child, and then having a parent with a serious mental illness, a parent or household family member with addiction, parental divorce, domestic violence in the home, or a household member incarcerated. I literally sit down with my patients and I actually score their number of adverse childhood experiences with them. I have two patients that have all 10. So one of my patients, she is the nicest person, has all 10. And she told me a story, and this is what her life was like as a child. Her dad had addiction to alcohol. So he was too intoxicated to do anything. There was no food in the house. And so she at age 11 had to get in the family car and drive to the store to buy food. So she started using drugs and alcohol around that same time because she was so overwhelmed as a child, she didn't know what to do. And the best way we can think of this is these are all stressful conditions. And our stress hormones are fantastic when it comes to running away from danger. But when our stress hormones are always active and always in our systems, that chronic stress changes how our brain grows and develops. And it also puts an extra stress on our organs. That's why we see it leading to things like heart disease. For context, my ACE score based on this is zero. And then the last part of it is post-traumatic stress disorder. So I'm assuming you guys have heard of PTSD. Yeah. So when I was a kid, it was something that we thought really only happened in soldiers. Like you went off to Vietnam and you were shot at in the jungle and you get nightmares and you can't sleep. It's actually more to the story. So I will tell all of you, I got diagnosed with post-traumatic stress disorder last year from my work as a doctor in the ER. I have seen stabbings, shootings, sexual assault, child abuse, hangings, overdoses, people crushed by cars. I still get flashbacks. And I thought having nightmares as a doctor was normal. So thank you, community hospital. They offered therapy for doctors. And I start, I signed up. I didn't know anything about therapy. And I got diagnosed with PTSD. And the reason I tell you that is the best way to think about PTSD is the I'm being chased by a bear response goes off at the wrong time. So again, if I'm being chased by a bear, I know that I will respond to be ready to fight or run to save my life. But when people live through a lot of traumas, it almost, you can think of it like a scar in their brain. And when they live through something that reminds them of that, the fight or flight response goes off at the wrong time. So I will literally be in clinic. I am safe. No one's gonna hurt me. And something will happen and I am all spun up and I can't figure out what's wrong. It's really weird. And a great number of my patients have PTSD, and that's a lot of why they use substances. I can't sleep because of nightmares, so I drink alcohol because it's a downer. And if I drink enough, I stop dreaming. You can imagine if you live through getting abused as a child, that's a really big risk factor for PTSD. Most of my patients that have these adverse childhood experiences, when I dig into it and I ask them, they have nightmares, they have flashbacks. And a lot of them are really just trying to figure out why I feel so bad and what do I do? And that's a lot of what I do as a doctor. I help them stop whatever drug they're using. I help them get into therapy. Literally, I sometimes buy books for art for my patients so they can journal when they're really stressed out. They make like workbooks for people with PTSD. And that's a lot of what I do as an addiction doctor is I help people who've been through really difficult things understand what they're feeling and stop using drugs and alcohol to cope. Okay. Now the last bit, and how are we on time? 1040?

unknown:

Yeah.

SPEAKER_00:

1040. Okay. The last thing is for you all to understand that your brain right now is still growing, and I'll explain how and why that matters. Okay. So there's maybe what, a hundred and say 120 people in your class? Does that sound right?

unknown:

Yeah.

SPEAKER_00:

120? Okay. So if we start using drugs and alcohol at a very young age, so let's imagine we're all in seventh grade. Okay. If we decide as a group, all of us as seventh graders are gonna just try out a bunch of drugs and alcohol, which obviously we wouldn't do, but two-thirds of us will develop addiction. So what is that like 90? 80, 90? Okay. Is anyone 15? Okay. So if we decide to start using drugs and alcohol around this age, 14 to 15, that number drops from two out of three to one out of four. So now we're looking at 30 people in this room if we all decide to try drugs and alcohol getting addicted. And if we wait till 21, that number drops to less than one in 10. So that's like maybe 10 or 11 of us. And the reason why this happens, there's two parts to it. Okay. The first is that when drugs and alcohol are in our brains, when we're young, the brain doesn't grow the same way. The brain does not reach its full potential. We actually have some pretty good studies on cannabis specifically. For high school students that use cannabis, they are less likely to get a B average, less likely to graduate high school, less likely to graduate college. The brain just does not grow to its full potential. The second part is that your brains do different things with dopamine than the adult brain. Remember, we talked about dopamine, it was going to be really important here. The teenage brain makes more dopamine when new stuff happens. So the first time you try alcohol when you're 15, it's actually more intense than if you wait till 21, because it makes more dopamine. And then the other thing about the teenage brain is that you actually have less dopamine on average than an adult. So if you ever wonder why it's so easy to get bored, it's actually the teenage brain does not make as much dopamine. So your brains are naturally going to look for new things to do. Again, whether it's social media, whether it's sports, whether it's bungee jumping, whether it's Reese's peanut butter cups, whether it's cocaine, your brain is constantly looking for more dopamine because as teenagers you make less at baseline. And then again, if you do try something new, you're gonna get a bigger spike. And then the last thing this is a man named Nick Chef, and he is in recovery from addiction. And his dad wrote about his addiction. The book was called Beautiful Boy, it was made into a movie. And this is actually one of his books about what it was like getting addicted. And the way he describes it, and I see this all the time, is drugs and alcohol offer a short-term solution to a problem. Like I feel anxious. If I use cannabis, I feel less anxious. And that's a lot of what my patients tell me. The problem is that I don't prescribe drugs and alcohol to patients because they cause long-term harm. So a lot of what I do as a doctor is I help people to, through therapy and medications, take those uncomfortable feelings and we manage them in a better way. But essentially what happens is his 13-year-old brain said, My parents are going through a divorce and I don't feel good. I'm anxious and I can't sleep. I know I'll use cannabis. And what happens is he started to view cannabis as his solution to everything. Okay. I feel bad, I'm gonna smoke. I feel good, I'm gonna celebrate by smoking. I'm really stressed out, I'm gonna smoke. I can't sleep, I'm gonna smoke. And so what we find is that when drug and alcohol use becomes regular, the brain stops growing socially and emotionally. So I literally get people who are like 40 years old, and if they started using drugs and alcohol at 18, when they get sober, they're emotionally still 18. And it's really hard for them because they don't know how to get a job, have a difficult conversation with a coworker, because the only thing they knew for all those years was drugs and alcohol. So literally, I'm gonna go back to work as a doctor. If I have a difficult patient encounter, I can't go chug a beer. I have to cope and move on with my day. And this is where we find that when people start using drugs and alcohol regularly in their teens, they don't get that full social and emotional potential. Okay. I can go through a case of what it actually looks like for one of my patients, or we can stop and do questions. What feels right? Case study? That's pretty good. Okay. All right. So this is one of my patients. I talked to her on Monday. So the way we learn as doctors is we do what are called case studies. So we literally describe a case and then you can learn from it. Okay. So this is my patient. She's 24 years old, and she was sent to me because she couldn't stop drinking alcohol. Okay. And I go through my usual stuff, like where are you from? What are your medical conditions? Do you have any allergies to medications? And so her only medical condition, because she's young, is that she has an alcohol addiction. She doesn't have any medications that she takes. And then I asked her about her use of drugs and alcohol. And she says that she would usually binge on alcohol, meaning drink a lot in a short period of time. And that alcohol would make her really sleepy because it's a downer. So she would use cocaine to wake up so she could drink more alcohol. So people sometimes mix uppers and downers to even out. Okay. And so as a doctor, I looked at what my options were and I started some medication for her to make alcohol feel less enjoyable. If you are wondering, we do make medications that make alcohol less enjoyable. And so I started her on the two medications. I saw her back in a month. She was still drinking. She'd maybe get a month where she wouldn't drink, and then she'd go back to drinking. And I just kept thinking, like, I feel like I'm missing something. So I about six months, you know, I said, let's talk about what we could be missing here. Why do you drink? And she was like, oh, what well, you know, I sometimes get really into it with my stepdad, and we fight and we argue and I don't know what to do. So and so we drink. And I was like, okay, well, let's unpack that. So I asked her, you know, did have you had any traumatic experiences? And she literally told me, Dr. Grover, no, I haven't. Not. And I was like, yeah, let's dig in a little more here. So I dug in deeper. I literally went through and asked her about all of those adverse childhood experiences. And it turns out that she had been verbally and physically abused by this stepdad for years. And then she also had a near fatal accident in a car when she was 19 that left her hospitalized for almost three weeks. And so I started to ask her, like, do you get nightmares? She was like, Dr. Grover, how do you know? I was like, Do you get flashbacks? And she's Dr. Grover, how do you know? And it turns out that she had post-traumatic stress disorder and I had missed it for the first six months of her care. And so we stopped what we were doing and we totally shifted. And I got her a therapist and I put her on medications specifically for post-traumatic stress disorder. And we started to make some progress. So I have her on three medications. She calls one of them trigger because she takes it when she's really physically upset. She calls one of them nightmare because she takes it to suppress her nightmares. And she all of a sudden had some tools, along with her therapist, was giving her tools. She had some tools to be able to say, I'm really upset. What am I gonna do? And so I saw her on Monday. She had been about six months sober, and she and her stepfather almost came to blows. So she had a little relapse, but it was like a few hours of drinking instead of a few days of drinking. And at the recommendation of her therapist, she moved out. And so she's away from that trigger. And so, yes, that that was my experience with her. I started focusing on the alcohol, but she's dual diagnosis. She has PTSD and alcohol addiction, and I had to treat both. Before we wrap up, a huge thank you to the Montage Health Foundation for backing my mission to create fun, engaging education on addiction. And a shout out to the nonprofit Central Coast Overdose Prevention for teaming up with me on this podcast. Our partnership helps me get the word out about how to treat addiction and prevent overdoses. To those healthcare providers out there treating patients with addiction, you're doing life-saving work and thank you for what you do. For everyone else tuning in, thank you for taking the time to learn about addiction. It's a fight we cannot win without awareness and action. There's still so much we can do to improve how addiction is treated. Together, we can make it happen. Thanks for listening. And remember, treating addiction saves lives.