How We Think Medicines Help ADHD

a. Why ADHD symptoms happen

Two key brain chemicals – dopamine and noradrenaline – play a big role in focus, attention, and reward.

• If these chemicals are too low in certain brain areas, the brain struggles to concentrate, stay calm, and control impulses.

• The frontal lobe, which manages attention and self-control, matures later than other parts of the brain. In ADHD, it may develop more slowly, leaving less “brake control” over behaviour.

• This can make people with ADHD feel restless, impulsive, and easily distracted.

• Sometimes the brain looks for extra stimulation to boost dopamine and noradrenaline — leading to risk-taking, reward-seeking, smoking, or chasing excitement.

• Genes matter too. For example, people with certain dopamine receptor genes may feel the effects of low dopamine more strongly.

b. How stimulant medicines work

Stimulants include methylphenidate (Ritalin, Concerta XL, Delmosart, Xaggatin, Xenidate), dexamfetamine (Amfexa) and lisdexamfetamine (Elvanse).

• In ADHD, some brain networks are underactive. This makes it hard to focus and leaves the brain “hungry” for stimulation.

• Stimulants block the recycling (reuptake) of dopamine and noradrenaline, meaning more of these chemicals stay in the brain.

• Amphetamine-based stimulants (like dexamfetamine and lisdexamfetamine) can also increase the release of these chemicals.

• This results in stronger signals between brain cells, which helps:

  • Improve focus

  • Reduce impulsive behaviour

  • Make the brain feel calmer and more balanced

c. Why stimulants can cause side effects

Boosting dopamine and noradrenaline is helpful in some brain areas — but too much in others can cause side effects such as:

• Loss of appetite

• Difficulty sleeping (especially if taken late in the day)

• Feeling nervous or restless

• Aggression (if the dose is too high)

• Faster heart rate (because noradrenaline also affects the heart)

d. How atomoxetine works (a non-stimulant)

Atomoxetine is different — it’s not a stimulant.

• It mainly works by increasing noradrenaline in the brain, especially in networks controlling attention, mood, and thinking.

• Boosting noradrenaline also gives a mild dopamine increase in some areas, which helps concentration without the risk of abuse.

• In simple terms, it strengthens the brain’s signals, helping people with ADHD focus and feel calmer.

e. Why atomoxetine can cause side effects

Because atomoxetine increases noradrenaline (and a little serotonin and dopamine), side effects can include:

• Poor sleep

• Nausea or vomiting

• Reduced appetite

• Faster heartbeat

Some people’s bodies break down atomoxetine differently depending on their CYP2D6 enzyme genetics:

• Slow metabolisers: higher drug levels → more side effects, even at low doses

• Ultra-fast metabolisers: lower drug levels → fewer side effects, but also less benefit

f. Key things to know about ADHD medicines

• Medicines don’t “cure” ADHD, but they can make a big difference in school, work, driving, and relationships.

• They don’t increase the risk of later drug misuse. In fact, by reducing impulsivity, they can make self-medication with alcohol, cannabis, or other drugs less likely.

• They don’t usually stop working — but doses may need adjusting as young people grow.

• Long-term side effects are not known to be a problem.

• Stimulants can usually be stopped and restarted safely if needed.

• For children and teenagers, medicines can help prevent lifelong difficulties in education, social skills, and employment.

👉 For further reading, see Brain and Mind Made Simple by Professor David Nutt, available via the Drug Science website.