Atomoxetine (Strattera is the best-known brand name for atomoxetine. Generic atomoxetine products are also widely available. In Canada)

What You Need to Know

Atomoxetine is a non-stimulant medication used primarily to treat attention-deficit/hyperactivity disorder (ADHD) in children, adolescents and adults. Unlike stimulant ADHD medications such as amphetamine or methylphenidate, atomoxetine primarily works by increasing the activity of norepinephrine in the brain.

It belongs to a medication class known as a selective norepinephrine reuptake inhibitor.

Atomoxetine can help improve:

• Attention
• Concentration
• Impulse control
• Organization
• Task completion
• Distractibility
• Hyperactivity and restlessness Atomoxetine is not a traditional stimulant and does not have the same abuse and dependence potential as amphetamine-based ADHD medications.

Its effects also develop differently. Stimulants can begin working within hours, whereas atomoxetine often requires several weeks of regular treatment before its full benefit becomes clear.

Atomoxetine is particularly important from a pharmacogenomic perspective because it is metabolized primarily by the liver enzyme CYP2D6. Genetic differences in CYP2D6 can produce substantial differences in atomoxetine exposure between patients.

What Is Atomoxetine Used For?

Atomoxetine is used primarily for:

• Attention-deficit/hyperactivity disorder (ADHD) in children
• ADHD in adolescents
• ADHD in adults Current U.S. prescribing information indicates atomoxetine for ADHD in adults and children 6 years of age and older.

Atomoxetine may be particularly considered when:

• A non-stimulant ADHD medication is preferred
• Stimulants have caused troublesome side effects
• A stimulant has not provided adequate benefit
• There are concerns about stimulant misuse or diversion
• Longer, smoother coverage throughout the day is desirable
• Certain coexisting symptoms make a non-stimulant option worth considering Medication choice should still be individualized to the person’s symptoms, medical history and previous treatment response.

How Does Atomoxetine Work?

Atomoxetine primarily blocks the norepinephrine transporter, often abbreviated NET.

NET normally removes norepinephrine from the space between nerve cells and carries it back into the neuron.

Atomoxetine partially blocks this recycling process.

The simplified pathway is:

1. Atomoxetine
2. Blocks norepinephrine transporter — NET
3. Less norepinephrine is recycled
4. More norepinephrine remains available for signaling
5. Attention and executive-function pathways are affected
6. ADHD symptoms may improve

Atomoxetine has particularly important effects in the prefrontal cortex, a region involved in:

• Attention
• Working memory
• Planning
• Organization
• Decision-making
• Impulse control Although atomoxetine primarily targets norepinephrine transport, NET also helps clear dopamine in the prefrontal cortex. Atomoxetine can therefore indirectly increase dopamine signaling in that region without producing the broader dopamine-releasing effect associated with stimulant medications.

What Are the Common Side Effects of Atomoxetine?

Side effects differ somewhat between children and adults.

Common side effects in children and adolescents include:

• Nausea

• Vomiting

• Reduced appetite

• Abdominal pain

• Fatigue

• Sleepiness

• Dizziness

• Headache Common side effects in adults include:

• Dry mouth

• Nausea

• Reduced appetite

• Constipation

• Dizziness

• Insomnia or sleep disturbance

• Fatigue

• Urinary hesitation

• Sexual side effects, including erectile dysfunction in some men Current prescribing information identifies nausea, vomiting, fatigue, decreased appetite, abdominal pain and somnolence among the most common pediatric effects; in adults, constipation, dry mouth, nausea, decreased appetite, dizziness, erectile dysfunction and urinary hesitation are among the most frequent.

Some adverse effects may be more likely when atomoxetine exposure is elevated, including in CYP2D6 Poor Metabolizers or when strong CYP2D6-inhibiting medications are being taken.

Atomoxetine carries an important warning regarding an increased risk of suicidal thoughts in pediatric patients.

Children and adolescents should be monitored for:

• New suicidal thoughts
• Worsening mood
• Significant behavioural changes
• Unusual agitation or emotional changes Monitoring is particularly important during the early months of treatment and following dose changes.

Blood Pressure and Heart Rate

Atomoxetine increases norepinephrine signaling and can increase:

• Heart rate

• Blood pressure Blood pressure and pulse should generally be measured:

• Before treatment

• Following dose increases

• Periodically during treatment Patients should seek medical attention for concerning symptoms such as:

• Chest pain

• Fainting

• Significant palpitations

• Unexplained shortness of breath Atomoxetine may not be appropriate for people with certain serious cardiovascular conditions.

• Liver Injury Rare cases of significant liver injury have been reported with atomoxetine.

Symptoms that should be discussed promptly with a healthcare professional include:

• Yellowing of the skin or eyes
• Dark urine
• Unexplained severe fatigue
• Upper abdominal pain
• Persistent nausea
• Unexplained itching Current prescribing information recommends discontinuing atomoxetine and not restarting it when jaundice or laboratory evidence of significant liver injury occurs.

Mania or Psychotic Symptoms

Atomoxetine can rarely produce or worsen:

• Mania
• Hallucinations
• Delusional thinking
• Severe behavioural disturbances Screening for bipolar disorder is recommended before treatment.

New manic or psychotic symptoms should be discussed promptly with the prescribing healthcare professional.

• Urinary Problems Atomoxetine can cause:

• Difficulty starting urination

• Urinary hesitation

• Urinary retention These effects are particularly relevant in adults and should be discussed with a healthcare professional if significant.

• Priapism Rare cases of priapism, a prolonged and sometimes painful erection, have occurred with atomoxetine.

An erection that persists for several hours requires urgent medical attention because untreated priapism can cause permanent tissue damage.

Growth in Children

Atomoxetine can reduce appetite and may temporarily affect weight gain or growth in some children.

Height and weight should therefore be monitored during long-term treatment.

Drug Interactions

Atomoxetine has several clinically important drug interactions.

MAO Inhibitors — Contraindicated

Examples include:

• Phenelzine
• Tranylcypromine
• Isocarboxazid
• Certain forms or doses of selegiline Atomoxetine should not be used together with an MAOI.

At least 14 days should generally separate stopping an MAOI and beginning atomoxetine, and at least 14 days should pass after stopping atomoxetine before starting an MAOI antidepressant.

Fluoxetine — Strong CYP2D6 Inhibitor

Atomoxetine is primarily metabolized by CYP2D6.

Fluoxetine strongly inhibits this enzyme.

Therefore:

1. Fluoxetine
2. CYP2D6 inhibition
3. Slower atomoxetine metabolism
4. Higher atomoxetine exposure
5. Potentially greater risk of side effects

The prescribing information specifically recommends slower titration when atomoxetine is taken with strong CYP2D6 inhibitors.

Paroxetine — Strong CYP2D6 Inhibitor

Paroxetine also strongly inhibits CYP2D6.

The same interaction can occur:

1. Paroxetine
2. Reduced CYP2D6 activity
3. Atomoxetine remains in the body longer
4. Atomoxetine exposure increases

Dose titration may therefore need to be slower.

• Bupropion — CYP2D6 Inhibitor Bupropion is another clinically important CYP2D6 inhibitor.

Although bupropion itself is primarily metabolized through CYP2B6, it can substantially inhibit CYP2D6.

Therefore:

Atomoxetine + bupropion

may result in:

1. Reduced CYP2D6 metabolism
2. Higher atomoxetine exposure

This is particularly important when the person already has genetically reduced CYP2D6 activity.

Quinidine — Strong CYP2D6 Inhibitor

Quinidine is a potent CYP2D6 inhibitor and is specifically identified in atomoxetine prescribing information.

It can substantially increase atomoxetine exposure by reducing its metabolism.

Blood Pressure Medications

Because atomoxetine can increase blood pressure, patients taking antihypertensive medications may require additional monitoring.

The response to blood-pressure medication may also need to be considered when atomoxetine is started or adjusted.

Albuterol and Other Beta-2 Agonists

Examples include:

• Albuterol
• Salbutamol These medications can also increase heart rate or blood pressure.

When combined with atomoxetine, cardiovascular effects may become more pronounced.

Current labeling recommends increased monitoring of heart rate and blood pressure when these medications are used together.

Dosage

Atomoxetine dosing depends particularly on body weight, age, CYP2D6 status, other medications and liver function.

It can be taken:

Once daily in the morning

or

Divided into two doses — morning and late afternoon/early evening.

Children and Adolescents Weighing Less Than 70 kg

Typical starting dose:

0.5 mg/kg/day

The usual target dose is:

1.2 mg/kg/day

The recommended maximum is:

1.4 mg/kg/day or 100 mg/day, whichever is less.

Children and Adolescents 70 kg or More and Adults

Typical starting dose:

40 mg/day

Usual target:

80 mg/day

Maximum:

100 mg/day

For patients without a CYP2D6-related reason for slower titration, the dose may generally be increased toward the target after a minimum of several days, depending on tolerability and the product-specific prescribing instructions.

Dosage for CYP2D6 Poor Metabolizers

CYP2D6 Poor Metabolizers process atomoxetine much more slowly.

Therefore dose increases should generally occur more cautiously.

For children under 70 kg who are known CYP2D6 Poor Metabolizers, current prescribing information recommends starting at:

0.5 mg/kg/day

and only increasing toward:

1.2 mg/kg/day

if symptoms remain inadequately controlled after approximately 4 weeks and the initial dose is well tolerated.

For adults and patients weighing at least 70 kg:

1. 40 mg/day
2. Only increase toward:

80 mg/day

after approximately 4 weeks if needed and well tolerated.

The same slower titration applies when taking a strong CYP2D6 inhibitor such as fluoxetine or paroxetine.

Dosage and Liver Function

Atomoxetine exposure increases when liver function is substantially impaired.

Current labeling recommends approximately:

• 50% of the normal dose for moderate hepatic impairment
• 25% of the normal dose for severe hepatic impairment Dose adjustments should be made by the prescribing healthcare professional.

Stopping Atomoxetine — Does It Need to Be Tapered?

Atomoxetine is different from many antidepressants.

Atomoxetine generally does not require a gradual taper before stopping.

Current Strattera prescribing information explicitly states:

No taper is needed when discontinuing atomoxetine.

This is because atomoxetine does not typically produce the same physiological withdrawal syndrome associated with some antidepressants, benzodiazepines or long-term high-dose stimulants.

However, that does not mean patients should automatically stop treatment on their own.

When atomoxetine is stopped:

• ADHD symptoms may return
• Concentration may worsen
• Impulsivity may increase
• Organization and task completion may deteriorate The decision to discontinue should therefore generally be discussed with the treating healthcare professional, particularly when the medication has been used successfully for an extended period.

Atomoxetine and Pharmacogenomic Testing

Atomoxetine has one of the best-established pharmacogenomic relationships among ADHD medications.

The most important gene is:

CYP2D6

CYP2D6 is the primary enzyme responsible for metabolizing atomoxetine.

Different people inherit different CYP2D6 variants and can therefore be classified as:

• Poor Metabolizers
• Intermediate Metabolizers
• Normal Metabolizers
• Ultrarapid Metabolizers These differences can have a large effect on atomoxetine concentration.

What Happens in a CYP2D6 Poor Metabolizer?

A CYP2D6 Poor Metabolizer has little or no functional CYP2D6 activity.

Therefore:

1. Atomoxetine
2. Very slow CYP2D6 metabolism
3. Atomoxetine remains in the body longer
4. Substantially higher atomoxetine exposure

Current prescribing information notes that CYP2D6 Poor Metabolizers have higher systemic atomoxetine exposure and may consequently have a greater risk of adverse reactions.

This is sufficiently important that the prescribing information provides specific dosing recommendations for CYP2D6 Poor Metabolizers.

Can Higher Atomoxetine Exposure Also Improve ADHD Response?

Interestingly, yes.

Atomoxetine is an unusual example where genetically slower metabolism can potentially produce:

More side effects

but also:

Greater therapeutic response in some patients who tolerate the medication.

CPIC notes that CYP2D6 Poor Metabolizers have substantially higher atomoxetine concentrations and, on average, can show greater improvement in ADHD symptoms than non-poor metabolizers, although they also have a greater likelihood of concentration-related adverse effects.

Therefore:

CYP2D6 Poor Metabolizer does not automatically mean atomoxetine is a bad medication.

It may mean that the patient needs lower or more cautiously titrated dosing.

What Happens in a CYP2D6 Ultrarapid Metabolizer?

A CYP2D6 Ultrarapid Metabolizer has unusually high CYP2D6 activity.

Therefore:

1. Atomoxetine
2. Very rapid metabolism
3. Lower atomoxetine concentration
4. Potentially inadequate exposure and reduced response

CPIC notes that CYP2D6 Ultrarapid Metabolizers may have difficulty achieving adequate atomoxetine concentrations at conventional doses.

This provides a possible explanation when someone takes an appropriate dose but experiences very little clinical effect.

Why Can Two People Taking the Same Atomoxetine Dose Respond Differently?

Consider two patients taking the same dose.

Patient A — CYP2D6 Poor Metabolizer

1. Slow metabolism
2. Higher concentration
3. Potentially:

Greater benefit + greater side-effect risk

Patient B — CYP2D6 Ultrarapid Metabolizer

1. Very fast metabolism
2. Lower concentration
3. Potentially:

Insufficient drug exposure + inadequate benefit

This is why CYP2D6 is particularly useful in understanding unexpected responses to atomoxetine.

Frequently Asked Questions

• Is Atomoxetine the Same as Strattera? Yes. Strattera is the original and best-known brand name for atomoxetine. Generic atomoxetine products are also available.

• Is Atomoxetine a Stimulant? No. Atomoxetine is a non-stimulant ADHD medication.

It primarily blocks norepinephrine reuptake rather than producing the neurotransmitter-releasing effects associated with amphetamine stimulants.

• Is Atomoxetine an Antidepressant? Atomoxetine acts on norepinephrine in a way that resembles some antidepressant mechanisms, but it is primarily approved and used as an ADHD medication, not as an antidepressant.

• What Does Atomoxetine Do to Norepinephrine? Atomoxetine blocks the norepinephrine transporter (NET).

This reduces norepinephrine recycling and allows more norepinephrine to remain available for signaling between nerve cells.

• Does Atomoxetine Increase Dopamine? Indirectly, in certain brain regions.

In the prefrontal cortex, NET helps remove both norepinephrine and dopamine. Blocking NET can therefore increase both neurotransmitters in this region.

Atomoxetine does not increase dopamine throughout the brain in the same way as amphetamine.

• How Long Does Atomoxetine Take to Work? Atomoxetine does not usually produce the immediate effect associated with stimulant medication.

Some improvement may become noticeable during the first few weeks, but the full therapeutic response can take several weeks, and continued improvement may occur beyond the first month.

• Why Does Atomoxetine Take Longer to Work Than a Stimulant? Stimulants rapidly increase dopamine and norepinephrine signaling.

Atomoxetine selectively blocks norepinephrine reuptake and appears to produce more gradual changes within attention and executive-function pathways.

The clinical benefit therefore tends to build over time rather than appearing within a few hours of the first dose.

• Does Atomoxetine Cause Insomnia? It can.

Some people experience insomnia or activation, while others experience sleepiness or fatigue.

The timing of dosing may therefore be individualized according to side effects and response.

• Does Atomoxetine Reduce Appetite? Yes.

Decreased appetite is a common side effect, especially in children and adolescents.

Weight and growth should be monitored during long-term treatment.

• Can Atomoxetine Cause Anxiety? Some people may experience nervousness, activation or increased anxiety, particularly when treatment begins or exposure is high.

For others, anxiety may improve as ADHD symptoms become better controlled.

• Can Atomoxetine Increase Blood Pressure? Yes.

Atomoxetine can increase heart rate and blood pressure because it increases norepinephrine signaling. Blood pressure and pulse should therefore be monitored.

• Does Atomoxetine Have an Addiction Risk? Atomoxetine is not a traditional stimulant and does not have the same abuse and dependence potential as amphetamine or methylphenidate.

It is therefore sometimes considered when stimulant misuse or diversion is a concern.

• Which Liver Enzyme Metabolizes Atomoxetine? The most important enzyme is:

CYP2D6

CYP2D6 genetic variation can substantially alter atomoxetine exposure.

• Can Fluoxetine Affect Atomoxetine? Yes.

Fluoxetine strongly inhibits CYP2D6 and can slow atomoxetine metabolism.

This can cause:

Higher atomoxetine exposure

and potentially:

More concentration-related side effects.

Slower dose titration is recommended when the drugs are combined.

• Can Paroxetine Affect Atomoxetine? Yes.

Paroxetine is another strong CYP2D6 inhibitor and can substantially increase atomoxetine exposure.

• Can Bupropion Affect Atomoxetine? Yes.

Bupropion inhibits CYP2D6 and may therefore reduce atomoxetine metabolism and increase its concentration.

This interaction is particularly important if the person already has genetically reduced CYP2D6 activity.

• Can Genetics Affect Atomoxetine Side Effects? Yes.

CYP2D6 Poor Metabolizers have substantially greater atomoxetine exposure than people with normal CYP2D6 metabolism.

Greater exposure can increase the likelihood of some side effects.

• Can Genetics Affect How Well Atomoxetine Works? Yes, potentially.

CYP2D6 affects atomoxetine concentration strongly enough that it can influence both tolerability and likelihood of response.

Poor Metabolizers may have higher concentrations and, when treatment is tolerated, may experience greater average symptom improvement.

Ultrarapid Metabolizers may have concentrations that are too low for an adequate response at standard dosing.

• Should I Change My Atomoxetine Dose Based on My CYP2D6 Result? No patient should change their dose independently.

However, unlike many psychiatric drug-gene relationships, CYP2D6 and atomoxetine have an established pharmacogenomic prescribing guideline.

A healthcare professional can use CYP2D6 information together with:

• Current dose

• ADHD symptoms

• Side effects

• Other medications

• CYP2D6 inhibitors

• Treatment duration

• Clinical response to determine whether the treatment strategy should be adjusted.

• Does Atomoxetine Need to Be Tapered? Usually no.

Current prescribing information states that atomoxetine can be discontinued without tapering.

However, stopping treatment can allow ADHD symptoms to return, so discontinuation should still be discussed with the prescribing healthcare professional.

• Can Pharmacogenomic Testing Tell Me Whether Atomoxetine Will Work? It cannot guarantee treatment success.

However, atomoxetine is one of the ADHD medications for which pharmacogenomic testing can provide particularly useful information because CYP2D6 has a major effect on drug exposure.

PGx testing may help explain why someone experiences:

Too much exposure → more side effects

or

Too little exposure → inadequate response

But medication response also depends on:

• ADHD symptom profile

• Dose

• Other medications

• Medical conditions

• Treatment duration

• Norepinephrine and dopamine biology

• Individual brain response Pharmacogenomic information should therefore support—not replace—clinical judgment.

• Why Pharmacogenomic Testing May Matter Atomoxetine provides a particularly clear example of the connection between genetics and medication exposure:

1. CYP2D6 genetics
2. CYP2D6 enzyme activity
3. Atomoxetine metabolism
4. Atomoxetine concentration
5. Effectiveness + side-effect risk

For some psychiatric medications, PGx information provides only limited evidence about dosing.

For atomoxetine, the relationship is stronger: CPIC has a dedicated CYP2D6–atomoxetine guideline, and current prescribing information also provides special dosing instructions for CYP2D6 Poor Metabolizers.

References

• [https://health-products.canada.ca/dpd-bdpp/search-fast-recherche-rapide?lang=eng&no=0150434007&wbdisable=true&no=0150434007&wbdisable=true)
• [https://files.cpicpgx.org/data/guideline/publication/atomoxetine/2019/30801677.pdf)
• [https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/021411s053lbl.pdf)
• [https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d4fe9217-1853-4f8b-9a93-77e511554ca1)
• [https://pmc.ncbi.nlm.nih.gov/articles/PMC4344948/)