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Odds are, you've heard of Ritalin or Adderall. They're both members of the class of drugs called stimulants, and they're often prescribed to treat attention deficit hyperactivity disorder, better known as ADHD.

But stimulants and hyperactivity seem like a weird match. If someone can't sit still, why would you give them more energy? Like with a lot of other psychiatric treatments, the answer has to do with a chemical imbalance in the brain.

The way stimulants affect that imbalance can reveal a lot about what's really happening when you get distracted or hyperactive — and what changes when you are focused and attentive. It can also explain why, if people without ADHD take these meds, they might not be getting the boost they think they are. ADHD doesn't look exactly the same in everybody, but most of the symptoms fall under one main category: executive functions, which are essentially the mental processes that help you get things done.

These include the qualities that usually come to mind when people think of ADHD, like focusing or remembering details. But the symptoms can include problems with other things, too, like organization, time management, and controlling your impulses and emotions. We haven't completely nailed down what's happening in the brains of people with ADHD, because looking directly into people's brains, turns out it's pretty hard.

But one of the main ideas is the low arousal theory, which basically says that people with. ADHD have chronically under-aroused brains, and that stimulants help by increasing their arousal. To be clear, arousal in this context just means less brain activity in certain regions.

When someone's brain is under-aroused, it can mean their neurons aren't firing as much in certain regions, or that some neurotransmitters, the chemicals that communicate signals between neurons, aren't flowing properly. According to the low arousal theory, this leads you to look for new stimulation in your environment to jump-start your neural activity. And from the outside, that looks like you're hyperactive or just inattentive.

More specifically, the disorder has to do with where you find dopamine, a neurotransmitter related to the brain's pleasure and reward responses. Generally, more dopamine translates to a greater feeling of reward. When your dopamine levels are high, you just feel … good.

One way to measure this is called the tonic dopamine level, which is how much dopamine is kind of hanging out between your neurons already. But there's also phasic dopamine, which is what your neurons release based on a stimulus — anything from finishing your PhD thesis to noticing the pretty bird outside your window. Both kinds of dopamine levels are important because they affect each other.

If you have a lot of tonic dopamine, for example, it can make the phasic response smaller. Neurons get a signal that there's already a lot of dopamine outside the cell, so they don't have to release as much when they try to send a signal to the next neuron. ADHD seems to do the opposite.

People with the disorder seem to have a lower level of tonic dopamine, meaning that the phasic responses are bigger. You might think that a bigger reward would be a good thing because it would increase your motivation. But that's not what happens.

The low arousal theory says that since there's less dopamine sitting between your neurons, you need much more stimulation to get it flowing the way it would in someone without ADHD. That translates to being hypersensitive to your environment. Dropping what you're doing to explore something new you just noticed becomes an almost impossible-to-resist urge.

And maybe you end up bouncing around a bunch to get more of those new and interesting things happening. That's where stimulant medications come in. They get more of that dopamine out between your neurons so you're not constantly looking for stimulants in your environment.

Now there are two major categories of stimulants used to treat

ADHD: there is methylphenidate, which is what's in Ritalin, and amphetamines, which take a few different forms in medications like Adderall and Vyvanse. No matter what category they're in, these stimulants target dopamine. Methylphenidate is a dopamine reuptake inhibitor, which means that when a neuron sends out some dopamine, the drug prevents it from collecting back whatever doesn't get picked up by the next neurons right away. Amphetamines work a little differently: instead of keeping neurons from collecting the dopamine they've already released, it stimulates them to release more of it.

But both types of stimulants specifically help increase tonic dopamine levels, by leaving more dopamine out between the cells. The idea is that this is closer to what's happening in a typical brain. Arousal goes up, and since there's plenty of tonic dopamine to go around, the phasic dopamine response gets smaller.

All of that leads to less of a need to get more stimulation from your environment, which makes it much easier to focus. So for a lot of people diagnosed with ADHD, these stimulants can help a lot. There are other treatment options, but they're generally less effective.

But their widespread availability leads to a lot of people using them recreationally — whether to help them study or by taking a large dose to get a high. That's a bad idea for all kinds of reasons. Both types of stimulants can cause addiction when you take higher doses or use them more often than prescribed, not to mention side effects like trouble sleeping and heart problems.

And if you don't have ADHD, they also … might not really have cognitive benefits. Not all studies agree on this, so we'll need more research to know for sure. But reviews published in 2011 and 2012 found only a few examples of these stimulants improving mental performance in people without ADHD.

And typically those were rote memory tasks, and only small improvements, and maybe only for some people who were recorded. In other cases, someone's performance only changed if they expected the drugs to improve their performance, which suggests that there's a placebo effect involved. Again, we don't know for sure that these meds don't help people without ADHD, so don't use this as a test to diagnose yourself or anything.

But stimulants work for ADHD because they change the chemistry of your brain to counteract the differences that cause problems with focus, along with all of those other executive functions. It's not about giving people more energy. And for people without ADHD, taking them might be risking some nasty side effects for the same thing they'd get from a placebo.

Thanks for watching this episode of SciShow Psych! For more about how psychiatric drugs can affect your brain, you can check out the episode where we debunked a bunch of misconceptions about antidepressants. [♪ OUTRO ].