Paroxetine
Is It Right for You?
A complete guide to Paroxetine — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Paroxetine?
Paroxetine is a selective serotonin reuptake inhibitor (SSRI) antidepressant with one of the broadest ranges of licensed indications among SSRIs. It is used to treat not only major depressive disorder but also a wide range of anxiety-related conditions, including obsessive-compulsive disorder, panic disorder, social anxiety disorder, post-traumatic stress disorder, and generalised anxiety disorder.
Paroxetine is among the most potent SSRIs and has additional pharmacological properties that distinguish it from other members of the class, including significant muscarinic acetylcholine receptor antagonism (accounting for its anticholinergic side-effect profile), mild inhibition of norepinephrine reuptake, and potent inhibition of the CYP2D6 enzyme — an important consideration for drug interactions.
Available in standard immediate-release tablets and controlled-release formulations (paroxetine CR), it is taken once daily, typically in the morning. Paroxetine is suitable for adults; it is not licensed for use in children and adolescents due to an unfavourable risk-benefit profile in this age group.
Paroxetine is a prescription-only medication in the UK. A licensed clinician must assess your symptoms and medical history before it can be prescribed — which can now be done quickly and conveniently through a telehealth consultation.
What Conditions Is Paroxetine Used For?
Paroxetine is licensed for a broad range of conditions:
including depression with associated anxiety.
intrusive thoughts and repetitive behaviours causing significant distress.
recurrent panic attacks with or without agoraphobia.
excessive fear of social scrutiny causing significant impairment.
persistent re-experiencing, avoidance, and hyperarousal following traumatic events.
excessive, uncontrollable worry and anxiety.
Paroxetine does not produce immediate relief. Most patients experience improvement in anxiety and mood symptoms over 2 to 4 weeks of treatment, with continued improvement over subsequent months. Do not discontinue treatment early if immediate effects are not felt.
How Does Paroxetine Work?
Paroxetine's primary mechanism of action is selective inhibition of the serotonin transporter (SERT), blocking the reuptake of serotonin from the synaptic cleft into the presynaptic neuron. This increases the availability of serotonin at postsynaptic receptors, enhancing serotonergic neurotransmission and producing antidepressant and anxiolytic effects over time.
Paroxetine is distinguished from other SSRIs by several additional pharmacological properties. Its significant muscarinic acetylcholine receptor antagonism contributes to side effects including dry mouth, constipation, urinary hesitancy, blurred vision, and weight gain. Its mild norepinephrine reuptake inhibition may contribute to its efficacy in certain anxiety and PTSD presentations.
Notably, paroxetine is a potent inhibitor of the CYP2D6 metabolic enzyme — which is responsible for the metabolism of a large number of commonly prescribed drugs. This property creates the potential for significant pharmacokinetic interactions with co-prescribed medications metabolised by this pathway.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Take paroxetine in the morning with or after breakfast, as taking it later in the day can cause insomnia. Food reduces the risk of nausea.
Take at the same time each day to maintain consistent blood levels and reduce the risk of missed-dose discontinuation symptoms.
Never stop paroxetine abruptly. Paroxetine has one of the most significant discontinuation syndromes among SSRIs due to its short half-life. Always taper the dose slowly — often over several weeks or months — under your clinician's supervision.
Allow 2 to 4 weeks for symptom improvement. Do not stop treatment early due to lack of immediate effect.
Tablets should be swallowed whole and not crushed or chewed. Controlled-release tablets must not be divided.
Side Effects of Paroxetine
Paroxetine is generally effective but carries a higher rate of some side effects — particularly sexual dysfunction, weight gain, and anticholinergic effects — than other SSRIs.
- Nausea (particularly at initiation)
- Dry mouth
- Constipation
- Somnolence (drowsiness)
- Sweating
- Headache
- Dizziness
- Sexual dysfunction (reduced libido, delayed or absent orgasm, ejaculatory delay — among the highest rates of any SSRI)
- Weight gain with long-term use
- Tremor
- Serotonin syndrome — agitation, confusion, fever, muscle rigidity, rapid heart rate; medical emergency
- Suicidal ideation — particularly in patients under 25 in the first weeks of treatment or following dose changes
- Severe discontinuation syndrome — if stopped abruptly; one of the most pronounced among all antidepressants
- Hyponatraemia — low sodium, causing confusion, seizures; particularly in elderly patients
- Mania activation — in patients with undiagnosed or known bipolar disorder
- Bleeding — gastrointestinal and other bleeding risk, particularly with concurrent NSAIDs or anticoagulants
- QT prolongation — paroxetine carries a low but recognised risk; avoid in patients with known QT prolongation
Paroxetine has a short half-life and causes one of the most severe and prolonged discontinuation syndromes of all antidepressants. Symptoms include electric shock sensations ("brain zaps"), dizziness, intense irritability, insomnia, flu-like symptoms, and vivid nightmares. Even missing a single dose can trigger symptoms. Tapering must be done very gradually — sometimes over months — and should always be done under clinical supervision. Never stop paroxetine suddenly.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting paroxetine. Paroxetine has a particularly complex interaction profile due to its CYP2D6 inhibition.
Paroxetine (via CYP2D6 inhibition) significantly increases blood levels of these antipsychotics, raising the risk of fatal cardiac arrhythmias. Concurrent use is contraindicated.
Paroxetine's potent CYP2D6 inhibition reduces the conversion of tamoxifen to its active metabolite endoxifen, potentially reducing its efficacy as a breast cancer treatment. Paroxetine should be avoided in patients receiving tamoxifen; alternative antidepressants with less CYP2D6 inhibition (e.g. venlafaxine, citalopram) are preferred.
Increased risk of serotonin syndrome.
CYP2D6 inhibition by paroxetine increases tricyclic plasma levels, potentially causing toxicity including cardiac arrhythmias.
Important Warnings
Paroxetine carries the highest risk of discontinuation syndrome among SSRIs. Never stop suddenly. Always taper slowly under clinical supervision, potentially over several months.
Paroxetine is the SSRI of most concern in pregnancy. Use in the first trimester has been associated with a small increased risk of congenital cardiac defects. Use in the third trimester has been associated with neonatal adaptation syndrome and persistent pulmonary hypertension of the newborn. Paroxetine should be avoided in pregnancy where possible, and alternative SSRIs are generally preferred.
Paroxetine is a potent CYP2D6 inhibitor and significantly affects the metabolism of many co-prescribed medications. A comprehensive medication review is essential before starting paroxetine
Paroxetine prescribed without a mood stabiliser in patients with undiagnosed bipolar disorder may precipitate a manic episode. Screen for bipolar disorder before initiating.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Paroxetine FAQs
Paroxetine has a very short half-life compared to other SSRIs (approximately 21 hours), meaning blood levels fall rapidly with missed doses or cessation. Additionally, paroxetine inhibits its own metabolism, so as the dose reduces, clearance speeds up, causing levels to drop faster than expected. This rapid decline triggers a discontinuation syndrome characterised by brain zaps, dizziness, irritability, and flu-like symptoms. A slow, careful taper — often over many weeks or months — is essential.
Paroxetine is associated with more weight gain than most other SSRIs, particularly with long-term use. This appears to be related to its anticholinergic properties and appetite-stimulating effects. Weight changes should be discussed with your clinician if they are a concern, and alternative agents may be considered.
Paroxetine should be used with caution in elderly patients. Its anticholinergic properties (dry mouth, urinary retention, constipation, cognitive effects) are more pronounced in this group. The risk of hyponatraemia (low sodium) and falls is also increased. A lower starting dose and careful monitoring are appropriate.
Yes. Paroxetine has one of the broadest sets of licensed indications among SSRIs, covering not only depression but also OCD, panic disorder, social anxiety disorder, PTSD, and generalised anxiety disorder. It is often chosen specifically because of its efficacy across multiple anxiety conditions.
All SSRIs share the same primary mechanism but differ in their additional pharmacological properties, half-lives, side-effect profiles, and interaction potential. Paroxetine has more anticholinergic side effects, more sexual dysfunction, and a greater discontinuation syndrome than most other SSRIs due to its short half-life. Fluoxetine, by contrast, has an extremely long half-life (and active metabolite), making discontinuation syndrome virtually negligible. Sertraline is often considered to have the most favourable overall tolerability and interaction profile.