How do stimulants (like Adderall) work?

Psychostimulants, or stimulants, are a class of drugs that increase alertness, arousal, wakefulness, and behavioral activity. Common examples include amphetamine, methylphenidate, cocaine, caffeine, nicotine, modafinil, and armodafinil.

These drugs produce varying degrees of sensory and motor activation, which is why they are classified as psychostimulants. While the history of stimulants is fascinating and stretches back centuries, that discussion is beyond the scope of this article.

Today, psychostimulants are prescribed for a variety of medical conditions, including attention-deficit/hyperactivity disorder (ADHD), narcolepsy, chronic fatigue, depression, and cancer-related fatigue. At the same time, several stimulants—including cocaine, methamphetamine, nicotine, and even caffeine—are commonly used recreationally and carry varying degrees of abuse potential.

To understand how these medications work, we first need to understand two important neurotransmitters: dopamine and norepinephrine.

Methylphenidate-based medications include Ritalin, Concerta, and Focalin.

Unlike amphetamine, methylphenidate does not directly promote neurotransmitter release. Instead, it works primarily by blocking the dopamine and norepinephrine transporters.

By preventing dopamine and norepinephrine from being removed from the synapse, methylphenidate increases their concentration in the synapse and prolongs their effects.

In this respect, methylphenidate works somewhat similarly to cocaine, although the pharmacokinetics, dosing, route of administration, and clinical effects are very different.

See the figure below.

Every second, your brain receives an overwhelming amount of sensory information. Yet only a tiny fraction reaches conscious awareness. While reading this sentence, your brain is processing information from your eyes, ears, muscles, joints, skin, internal organs, and countless other sources. Most of this information never reaches awareness because it is irrelevant to your current goals.

For example, before reading this paragraph, were you actively aware of your left big toe?

Probably not.

The sensory signals from your toe never disappeared. Your brain simply determined they were unimportant and filtered them out. This filtering process is one of the brain’s most important jobs. Much of the brain’s energy is spent deciding what deserves attention and what can safely be ignored.

The Piano Tuner Analogy

One way to think about dopamine and norepinephrine is to imagine a piano. The strings of the piano represent the major excitatory and inhibitory networks of the brain—primarily glutamate and GABA neurons.

Dopamine and norepinephrine are not the music itself. They are the piano tuners. Their job is to tighten or loosen the strings so the music sounds right.

If the strings are too loose, the music becomes muddy and disorganized. If the strings are too tight, the sound becomes distorted.

Similarly, dopamine and norepinephrine help tune neural networks so the brain can focus on what matters while ignoring distractions.

Norepinephrine: Enhancing the Signal

In the prefrontal cortex—the region of the brain responsible for attention, planning, decision-making, and self-control—norepinephrine helps strengthen relevant signals.

At moderate levels, norepinephrine preferentially stimulates α2A receptors, improving focus and working memory.

However, as norepinephrine levels continue to rise, other receptors (α1 and β receptors) become activated.

This is where problems begin.

Excessive norepinephrine is associated with stress and the fight-or-flight response. Under these conditions, attention becomes fragmented, impulsive, and less efficient.

From an evolutionary perspective, this makes sense.

If a lion is chasing you, your brain should focus on survival rather than the details of a spreadsheet.

As a result, the relationship between norepinephrine and attention follows an inverted-U pattern:

• Too little norepinephrine → poor alertness and weak focus
• Moderate norepinephrine → optimal attention
• Too much norepinephrine → impaired focus and increased anxiety

So…when the NE concentration is too low, the signal strength (i.e., our ability to focus on things) is low. But as the NE concentration increases so does the signal strength (i.e., our ability to focus on things) until it reaches a peak. After that, any additional increase in NE impairs our ability to focus.

This explains the inverted U shaped curves depicted below.

Dopamine: Reducing the Noise

While norepinephrine helps strengthen important signals, dopamine helps suppress irrelevant ones.

In the prefrontal cortex, dopamine acts primarily through D1 receptors to filter out distractions.

When dopamine levels are too low, everything appears equally important. Relevant and irrelevant information compete for attention, making it difficult to stay focused on a single task.

As dopamine levels rise into an optimal range, irrelevant signals are filtered out more effectively. The brain becomes better able to focus on what matters while ignoring distractions.

However, too much dopamine creates a different problem.

Excessive dopamine stimulation can lead to rigid attention, hyperfocus, impulsivity, and impaired cognitive flexibility. In some situations, individuals become intensely focused on activities that may not actually be productive.

Stress, recreational drug use, and excessive stimulant exposure can all push dopamine levels beyond their optimal range.

Like norepinephrine, dopamine follows its own inverted-U relationship with performance.

Why Stimulants Help ADHD

This is where stimulant medications become clinically useful.

Medications such as:

• Amphetamine (Adderall, Vyvanse, Dexedrine)
• Methylphenidate (Ritalin, Concerta, Focalin)
• Bupropion (Wellbutrin)
• Atomoxetine (Strattera)

all influence dopamine and/or norepinephrine signaling.

Their therapeutic benefit comes not from “speeding up” the brain but from helping neural networks function within their optimal range. Norepinephrine helps enhance important signals. Dopamine helps suppress irrelevant noise.

Together, they improve the brain’s ability to prioritize information, sustain attention, and regulate behavior.

The Goldilocks Principle

When it comes to dopamine and norepinephrine, more is not always better.

Too little dopamine may contribute to apathy, low motivation, anhedonia, and poor concentration. Too much dopamine may contribute to hyperfocus, compulsive behavior, euphoria, and addiction.

Too little norepinephrine may contribute to fatigue, drowsiness, low energy, and difficulty concentrating. Too much norepinephrine may produce anxiety, hypervigilance, sweating, palpitations, and other symptoms associated with the fight-or-flight response.

The goal is not maximal stimulation. The goal is optimal stimulation.

Like Goldilocks, the brain functions best when dopamine and norepinephrine are neither too high nor too low—but just right.

This is why carefully prescribed stimulant medications can be remarkably effective for some individuals. Rather than simply increasing activity in the brain, they help tune neural networks so that important signals stand out while irrelevant distractions fade into the background.