How Do ADHD Medicines Work? Stimulants and Non-Stimulants Explained

In short: ADHD medicines are thought to work mainly by increasing the activity of two brain chemical messengers, dopamine and noradrenaline, in networks that control attention, planning and impulse control. Stimulants (methylphenidate, lisdexamfetamine and dexamfetamine) act quickly, while non-stimulants (atomoxetine and guanfacine) work in different ways and build up over several weeks. Medicines do not cure ADHD, but for many people they reduce symptoms enough to make day-to-day life easier, alongside other support.

This guide, written by a Ready Health prescribing pharmacist, explains in plain English how ADHD medicines are believed to work, why side effects happen and how treatment is monitored in the UK.

What is happening in the brain in ADHD?

ADHD is a neurodevelopmental condition, which means it relates to how the brain develops and functions. Research suggests that brain networks responsible for focus, organisation, working memory and self-control can be less active or less efficiently connected in people with ADHD. Dopamine and noradrenaline help carry signals within these networks, and differences in how they are released and recycled are thought to be part of the picture.

The areas at the front of the brain that help us plan, pause and prioritise tend to mature later in people with ADHD. This can show up as restlessness, distractibility, acting before thinking, or seeking stimulation and novelty. ADHD runs strongly in families, and many genes, each with a small effect, are involved; no single gene causes it.

How do stimulant ADHD medicines work?

The stimulants used in the UK are methylphenidate, lisdexamfetamine and dexamfetamine. They come in short-acting and long-acting forms.

• Methylphenidate mainly blocks the reuptake (recycling) of dopamine and noradrenaline, so more of these messengers stay active between nerve cells.
• Lisdexamfetamine and dexamfetamine block reuptake and also encourage the release of dopamine and noradrenaline. Lisdexamfetamine is a "prodrug" that the body gradually converts into dexamfetamine, giving a smoother, longer effect.

Stronger signalling in attention and control networks can help people concentrate for longer, organise tasks and manage impulses. Effects are usually noticeable within hours of a dose, which is why stimulants are carefully adjusted (titrated) over a few weeks to find the right dose.

Why do stimulants cause side effects?

Dopamine and noradrenaline act throughout the body, not only in the networks involved in ADHD. Raising them elsewhere explains the most common side effects:

• reduced appetite and weight loss;
• difficulty getting to sleep, particularly if a dose is taken late in the day;
• headache, stomach ache, feeling anxious, irritable or low;
• increased heart rate and blood pressure.

Many side effects ease after the first few weeks or improve with dose or timing changes. Stimulants are Controlled Drugs in the UK because they can be misused, so prescriptions are closely managed.

How do non-stimulant ADHD medicines work?

Atomoxetine blocks the reuptake of noradrenaline. In the front of the brain this also raises dopamine levels indirectly, which is thought to help attention. It is not a Controlled Drug and has a low potential for misuse. It is taken every day and its benefits build up over several weeks rather than hours.

Guanfacine works differently again. It stimulates specific receptors (alpha-2A receptors) on nerve cells in the front of the brain, strengthening the signals that help with attention and impulse control. It also lowers blood pressure and heart rate, so it must not be stopped suddenly.

Why do non-stimulants cause side effects?

• Atomoxetine: nausea, reduced appetite, stomach upset, sleep problems, raised heart rate and blood pressure. Rarely, it can affect the liver, and prescribers watch for changes in mood or thoughts of self-harm, particularly early in treatment.
• Guanfacine: sleepiness, tiredness, dizziness, low blood pressure and slow heart rate.

People break down atomoxetine at different speeds because of variation in a liver enzyme called CYP2D6. Slow metabolisers have higher blood levels and may notice more side effects, and some other medicines (for example fluoxetine or paroxetine) can have the same effect. This is one reason why every medicine you take should be reviewed by your prescriber.

Stimulants and non-stimulants compared

How is ADHD medicine monitored in the UK?

NICE guidance (NG87) recommends that ADHD medicines are started by a specialist, with a check of heart health, blood pressure, pulse, weight and (in children) height before treatment. These are then monitored during dose changes and regularly afterwards, with at least a yearly review of whether medicine is still needed. Once stable, prescribing may be shared with a GP under a shared care agreement.

What should I know about taking ADHD medicines long term?

• Medicine is one part of treatment. Psychoeducation, environmental changes, coaching and talking therapies can all help.
• Good evidence suggests treating ADHD does not increase the risk of later substance misuse, and may reduce it by easing impulsivity.
• Doses sometimes need adjusting over time, for example as children grow.
• Growth, weight, blood pressure and heart rate are monitored because these can be affected over longer periods.
• Some people take planned breaks; this should always be agreed with your prescriber.

Frequently asked questions

Do ADHD medicines change your personality?

They should not. If you feel flat, emotionless or "not yourself", tell your prescriber, as this can be a sign the dose or medicine needs changing.

How quickly do ADHD medicines work?

Stimulants usually work within an hour or two of a dose. Atomoxetine and guanfacine take several weeks to reach their full effect.

Are ADHD medicines addictive?

Stimulants can be misused, especially if taken in ways other than prescribed, which is why they are Controlled Drugs. When taken as prescribed and monitored, the risk of dependence is low.

Can I drink alcohol while taking ADHD medicine?

Alcohol can worsen side effects and ADHD symptoms. Ask your prescriber or pharmacist for advice that applies to your medicine.

Key takeaways

• ADHD medicines mainly boost dopamine and noradrenaline signalling in attention and self-control networks.
• Stimulants act within hours; non-stimulants build up over weeks.
• Side effects reflect the same chemicals acting elsewhere in the body, such as appetite, sleep and the heart.
• Treatment is started by a specialist and monitored regularly, in line with NICE guidance.
• Medicine works best as part of a wider support plan.

Sources and further reading

• NICE NG87: Attention deficit hyperactivity disorder: diagnosis and management
• BNF: Attention deficit hyperactivity disorder treatment summary
• NHS: ADHD treatment

Last reviewed: October 2026 by Shamir Patel, Independent Prescribing Pharmacist, Ready Health. This article is general information and does not replace advice from your own clinician. Brand names are trademarks of their respective owners.

If you would like to explore whether you have ADHD, or need a specialist review, learn about our ADHD assessment service in Standish, Wigan. Any decision about medicine is made by a prescriber after a full assessment.