CNS stimulants: why they matter
Central nervous system (CNS) stimulants increase alertness, attention or wakefulness. They include prescribed medicines for attention-deficit/hyperactivity disorder (ADHD) and narcolepsy, as well as substances with major misuse potential. Their benefit depends on selecting the right diagnosis, using one formulation correctly, and monitoring cardiovascular, sleep, growth, psychiatric and misuse risks.
Learning outcomes: classify stimulants; explain their mechanisms; use indicative dose/titration tables safely; recognise toxicity; and counsel patients about diversion and sleep hygiene.
Use the dose table safely
Doses below are common adult teaching ranges, not a substitute for the product label or local protocol. Confirm the exact formulation (immediate versus modified release), indication, age, comorbidity, interacting medicines and controlled-drug requirements before prescribing. Start low, titrate one product at a time, and document response and adverse effects.
1. Classification and mechanisms
| Group | Examples | Core pharmacology |
|---|---|---|
| Amphetamine-type stimulants | Dexamfetamine, lisdexamfetamine, amphetamine | Increase synaptic dopamine and noradrenaline largely by promoting release and reversing transporters. |
| Methylphenidate-type | Methylphenidate | Inhibits dopamine and noradrenaline reuptake transporters, increasing synaptic availability. |
| Wakefulness-promoting agents | Modafinil, armodafinil | Mechanism is not fully defined; promotes wakefulness through several neurotransmitter systems and has interaction potential. |
| Methylxanthines | Caffeine, theophylline | Adenosine-receptor antagonism; at higher exposures also affects phosphodiesterase activity and calcium handling. |
| Historical/limited-use stimulants | Cocaine, ephedrine and others | Important for toxicology and misuse teaching; not routine long-term treatment choices. |
In ADHD, improving signalling in prefrontal networks can improve attention and impulse control. This is not the same as giving a stimulant to a healthy person for “study power”: higher exposure can worsen anxiety, insomnia, hypertension, psychosis and dependence without improving learning.
2. Clinical uses
- ADHD: part of a structured plan that includes diagnostic assessment, functional goals, education and behavioural support.
- Narcolepsy/excessive daytime sleepiness: selected wakefulness-promoting medicines or stimulants after sleep-disorder evaluation.
- Apnoea of prematurity: caffeine citrate is used in neonatal protocols—this is specialist neonatal prescribing, not an adult caffeine dose extrapolation.
- Other uses: some indications are country- and product-specific; do not assume that a drug approved for one indication is suitable for another.
3. Dose and formulation table
| Medicine | Typical adult starting and titration approach | Usual ceiling / practical checks |
|---|---|---|
| Methylphenidate immediate release | Product-dependent. A common adult regimen is divided oral doses 2–3 times daily, with individual titration. Give earlier in the day to reduce insomnia. | Many immediate-release labels describe 20–30 mg/day as an average adult total and a maximum of 60 mg/day; modified-release products have different limits. Never interchange mg-for-mg without checking the formulation. |
| Lisdexamfetamine | Common ADHD labels start once-daily morning treatment at 30 mg and titrate at weekly intervals if needed. | Typical labelled maximum 70 mg/day. Review pulse, blood pressure, appetite, sleep and psychiatric symptoms at each increase. |
| Dexamfetamine | Use a low morning dose and titrate cautiously in divided doses according to local ADHD/narcolepsy guidance. | Exact maximum varies by indication and product. Avoid late dosing and avoid co-prescribing duplicate stimulant products unless specialist-directed. |
| Modafinil | For adult narcolepsy, many labels use 200 mg orally in the morning; some divide morning/noon dosing. | Higher doses are not automatically more effective. Review hormonal-contraception interactions, rash, psychiatric history and hepatic impairment. |
| Caffeine | Dietary caffeine is not prescribed like ADHD medicine. Assess total daily intake from coffee, energy drinks, tablets and combination analgesics. | High intake can produce tremor, anxiety, insomnia, tachycardia and arrhythmia. Do not use adult “energy” doses for neonates or children. |
4. Baseline assessment before prescribing
| Check | Reason |
|---|---|
| Diagnosis, functional impairment and treatment goal | Prevents symptom-only prescribing and provides a measurable review target. |
| Pulse, blood pressure, weight; cardiovascular history and family history of sudden death/arrhythmia | Stimulants may increase pulse/BP and can be unsafe in serious structural heart disease or important arrhythmia. |
| Sleep, anxiety, depression, mania, psychosis and tics | Stimulants can worsen insomnia, anxiety and psychotic/manic symptoms. |
| Substance use, diversion risk and safeguarding | Misuse, snorting/injecting, sharing tablets and coercion can cause harm and legal consequences. |
| Pregnancy potential, lactation, renal/hepatic disease and full medicine list | Changes drug choice, dose, interaction risk and counselling. |
5. Adverse effects, interactions and toxicity
Common adverse effects are reduced appetite, weight loss, headache, dry mouth, nausea, tremor, sweating, anxiety, insomnia, tachycardia and raised blood pressure. Important but less common harms include chest pain, arrhythmia, severe hypertension, peripheral vasculopathy, hallucinations, mania or psychosis. Assess new suicidal thinking or marked behavioural change promptly.
Dangerous interactions include monoamine oxidase inhibitors (MAOIs), other sympathomimetics, some decongestants and medicines that independently raise heart rate or blood pressure. Modafinil can reduce the reliability of hormonal contraception through enzyme induction; check the current product information and discuss an effective alternative during treatment and for the recommended period after stopping.
Stimulant overdose: initial management
Suspect overdose with severe agitation, panic, hyperthermia, hypertension, tachyarrhythmia, chest pain, seizures, delirium or rhabdomyolysis. Use ABCDE assessment, check glucose/temperature/ECG, manage agitation and seizures according to emergency protocol, cool hyperthermia, treat complications and contact toxicology/critical-care support. Do not leave an agitated, hyperthermic patient unmonitored.
6. Dependence, diversion and patient counselling
- Explain that tablets must never be shared, sold, crushed, snorted or injected.
- Use the lowest effective dose and review regularly; treatment is not “set and forget.”
- Take morning/early-day doses as directed; avoid extra caffeine and ask before using cold remedies or supplements.
- Seek urgent care for chest pain, fainting, severe headache, hallucinations, suicidal thoughts or suspected overdose.
- Store controlled medicines securely and count remaining tablets when diversion is a concern.
7. OSCE and exam points
OSCE structure: confirm the indication and formulation; measure BP, pulse and weight; ask about sleep, appetite, mood, psychosis and substance use; screen for interacting medicines; agree a functional target; explain timing, storage and red flags; schedule review after each titration. In an exam, distinguish methylphenidate reuptake blockade from amphetamine-promoted catecholamine release.
