Antidepressants are the third most dispensed medicine class in England, with over 85 million items prescribed in 2023–24 according to NHSBSA data. Selective serotonin reuptake inhibitors (SSRIs) and serotonin-noradrenaline reuptake inhibitors (SNRIs) account for the majority of new prescriptions. Community pharmacists dispense these medicines daily — and the quality of the counselling conversation at initiation can significantly influence whether a patient continues treatment long enough to benefit.
Why pharmacy counselling matters
NICE guideline CG90 (updated as NG222) on depression in adults recommends that patients starting antidepressants receive clear information about expected onset of action, side effects, and the importance of continuing treatment even after symptoms improve. In practice, GP consultations that result in an antidepressant prescription are often time-pressured, and the patient may leave the surgery with limited understanding of what to expect.
The pharmacy dispensing interaction — where the patient physically receives the medicine — is the natural moment to fill this information gap. The New Medicine Service (NMS) provides a structured framework for follow-up, and antidepressants are among the most common NMS-eligible categories.
The medicines: what pharmacists dispense most
SSRIs
| Medicine | Typical starting dose | Key counselling points |
|---|---|---|
| Sertraline | 50mg once daily | First-line choice in NICE guidelines. GI side effects common initially. |
| Citalopram | 10–20mg once daily | QTc prolongation risk — max 40mg (20mg if over 65 or hepatic impairment). |
| Fluoxetine | 20mg once daily | Long half-life (advantage for missed doses, disadvantage for drug interactions). |
| Escitalopram | 5–10mg once daily | S-enantiomer of citalopram. QTc risk applies. |
| Paroxetine | 20mg once daily | Higher withdrawal symptom risk than other SSRIs. Strongest anticholinergic effects in the class. |
SNRIs
| Medicine | Typical starting dose | Key counselling points |
|---|---|---|
| Venlafaxine | 37.5–75mg once daily (XL) | Monitor blood pressure — dose-related hypertension. |
| Duloxetine | 30–60mg once daily | Also licensed for neuropathic pain and stress urinary incontinence. Nausea common initially. |
Essential counselling at initiation
The first dispensing of an antidepressant is the most critical counselling opportunity. Key messages to convey:
1. Onset of action
"This medicine takes 2 to 4 weeks to start working. You may feel some side effects before you feel any benefit. This is normal and does not mean the medicine is not working."
This is perhaps the single most important piece of information. Patients who expect immediate relief are far more likely to stop prematurely. The delayed onset of action is a consistent feature of all SSRIs and SNRIs, related to the time required for neuroplastic changes rather than simple neurotransmitter reuptake inhibition.
2. Early side effects
"In the first 1–2 weeks, you may notice nausea, headache, difficulty sleeping, or feeling more anxious. These symptoms usually settle. If they are troublesome, call us or speak to your GP — there are things we can suggest."
Common early side effects include:
- Nausea — taking the medicine with food can help; usually resolves within 1–2 weeks
- Insomnia or drowsiness — timing can be adjusted (morning dose if drowsy; evening if insomnia, or vice versa depending on the medicine)
- Increased anxiety — paradoxical initial increase, particularly with sertraline and fluoxetine; usually transient
- Sexual dysfunction — may emerge later (weeks to months); affects libido, arousal and orgasm; often under-reported by patients. Pharmacists should mention this proactively, as it is a leading cause of long-term non-adherence
3. Duration of treatment
"Once you start feeling better, your GP will usually recommend continuing for at least 6 months after recovery to reduce the risk of relapse. Do not stop without discussing it with your GP or pharmacist."
NICE recommends a minimum of 6 months continuation treatment after remission of a first episode, and longer for recurrent depression. Patients often assume they should stop once they feel well — the protective value of continuation therapy is not intuitive and needs reinforcing.
4. Do not stop suddenly
"When the time comes to stop, your GP will reduce the dose gradually. Stopping suddenly can cause withdrawal symptoms — dizziness, nausea, anxiety, flu-like feelings, electric shock sensations. These are not dangerous but they are unpleasant and avoidable with a slow taper."
NICE NG222 now recommends gradual dose reduction over weeks to months, depending on the duration of treatment and the specific medicine. Paroxetine and venlafaxine carry the highest withdrawal risk. Fluoxetine, with its long half-life, carries the lowest.
The NMS opportunity
Antidepressants are ideally suited to the New Medicine Service structure:
- Day 7–14 follow-up: Are side effects manageable? Is the patient still taking the medicine? Any concerns?
- Day 21–28 follow-up: Is there any early benefit? Is adherence maintained? Any emerging side effects (particularly sexual dysfunction, which may take longer to manifest)?
The NMS evaluation data shows significantly better adherence outcomes for patients receiving the service. For a medicine where the therapeutic effect is delayed and early side effects are common, this structured follow-up is particularly valuable.
Drug interactions to watch
SSRIs and SNRIs have clinically significant interactions that pharmacy teams should screen for:
| Interaction | Risk | Action |
|---|---|---|
| SSRIs/SNRIs + MAOIs | Serotonin syndrome (potentially fatal) | Absolute contraindication. 2-week washout required (5 weeks for fluoxetine). |
| SSRIs/SNRIs + triptans | Serotonin syndrome risk (lower than MAOIs) | MHRA advises caution; monitor for symptoms. |
| SSRIs + NSAIDs | Increased GI bleeding risk | Consider gastroprotection (PPI) if concurrent use is necessary. |
| Fluoxetine/paroxetine + tamoxifen | Reduced tamoxifen efficacy (CYP2D6 inhibition) | Switch to sertraline or citalopram. |
| Citalopram/escitalopram + other QTc-prolonging drugs | QTc prolongation, arrhythmia risk | Avoid combination or monitor ECG. |
| Venlafaxine + CYP3A4 inhibitors | Increased venlafaxine levels | Monitor for hypertension and serotonergic symptoms. |
Serotonin syndrome: recognition
Pharmacy teams should be aware of serotonin syndrome symptoms, particularly when dispensing combinations of serotonergic medicines:
- Agitation, confusion, restlessness
- Rapid heart rate, hypertension, hyperthermia
- Muscle rigidity, tremor, hyperreflexia, clonus
- Diarrhoea, nausea
Onset is usually within hours of starting or increasing a serotonergic medicine. It is a medical emergency — advise the patient to seek immediate medical attention (A&E or 999).
When to refer
Pharmacy teams should refer patients to their GP or mental health services when:
- Suicidal ideation is expressed (assess urgency — if immediate risk, call 999 or Samaritans 116 123)
- Symptoms have not improved after 4–6 weeks at an adequate dose
- Side effects are intolerable and the patient wants to stop
- The patient is requesting to stop treatment prematurely
- Pregnancy is planned or confirmed (some SSRIs are preferred over others; specialist review needed)
- Complex polypharmacy with serotonergic risk
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Sources
- NICE NG222: Depression in adults — treatment and management (2022).
- NHSBSA. Prescription cost analysis, England 2023–24.
- MHRA Drug Safety Update: SSRIs and SNRIs — serotonin syndrome risk.
- BNF: Individual drug monographs for sertraline, citalopram, fluoxetine, escitalopram, paroxetine, venlafaxine, duloxetine.
- NHS England. Community Pharmacy Contractual Framework — NMS specification.
- PharmSee pharmacy data: pharmsee.co.uk.