Key takeaways
- ACE describes some improvement from two weeks and full benefit typically at 4 to 12 weeks. Early side effects and the medicine’s sleep, appetite, sexual and cardiovascular effects need review during that period. ACE
- HealthHub highlights new or worsening self-harm thoughts and agitation particularly in people under 25 and during the first weeks of treatment changes. Report these or manic symptoms promptly. HealthHub
- Withdrawal may follow missed doses or rapid stopping. NICE calls for particular care with paroxetine and venlafaxine; a reduction plan may take weeks or months. NICE
Antidepressant classes: onset, side effects and stopping questions
NICE’s adult depression guidance schedules the first medicine review usually within 2 weeks. For a new prescription in someone aged 18 to 25, or where suicide risk is a particular concern, it specifies 1 week. That appointment checks symptoms and side effects while treatment is still getting started.
What does an antidepressant class tell you?
It describes some of the medicine’s pharmacology, without predicting your whole experience. Singapore’s Agency for Care Effectiveness (ACE) groups SSRIs, SNRIs and newer agents as second-generation antidepressants. It prefers these for routine first-line medicine treatment of major depressive disorder. TCAs and MAOIs have a narrower margin between effective and toxic amounts, with greater potential toxicity.
ACE lists adverse effects, contraindications, interactions and cost among selection factors. Most efficacy differences between locally registered options are small or uncertain; previous response and effects on daily life may matter more. The guideline does not recommend routine pharmacogenomic testing to select treatment for newly diagnosed depression: it describes inconsistent, low-certainty evidence affected by lack of blinding.
| Class or example | Common comparison questions | Important cautions to discuss |
|---|---|---|
| SSRIs: escitalopram, sertraline, fluoxetine, paroxetine | Nausea, sleep, restlessness and sexual effects; interactions; prior response | Bleeding risk, low sodium, serotonin syndrome, mania risk and medicine-specific withdrawal |
| SNRIs: venlafaxine, duloxetine | Similar serotonergic effects plus whether pain symptoms or another indication matters | Blood pressure or heart rate, liver or kidney considerations, interactions and withdrawal |
| Mirtazapine | Whether sleep, appetite or weight effects fit or conflict with the person’s needs | Drowsiness, increased appetite, weight gain and impaired alertness |
| TCAs: amitriptyline and others | Whether there is a specific reason an older medicine is being used | Anticholinergic effects, falls, rhythm risk and greater danger in overdose |
| MAOIs | Specialist use after other options or for selected presentations | Major food and medicine interactions; switching needs specialist planning |
Discuss the table with the prescriber; anxiety, pain and other indications change the comparison.
How long should benefit take?
Some improvement can appear within two weeks; full benefit often takes longer. ACE gives about 4 to 12 weeks for full benefit. NICE says an effect is usually seen within four weeks if the medicine is going to work. Neither range guarantees an individual’s response or replaces early follow-up.
ACE suggests tracking symptom scores, for example with PHQ-9, along with adverse effects. Keep everyday changes in the record too: getting out of bed, concentration, returning to routine, spending time with people and taking interest in things. Sleep, appetite, nausea, agitation or anxiety may change before those parts of recovery.
Before changing treatment for limited response, ACE asks clinicians to check adherence, ongoing stressors, side effects, diagnosis and medical conditions. Anaemia, thyroid disease, substance use, bipolar disorder and interacting medicines can change the next step. Feeling better also does not end the course: ACE recommends continuing antidepressant treatment for at least 6 months after remission, followed by a shared decision about further treatment.
Why do side effects differ within and between classes?
Different medicines can disturb sleep, appetite and physical function in different ways. Serotonin effects include nausea, diarrhoea, sweating, tremor, sleep disturbance and sexual difficulties. SNRIs also have noradrenergic effects that can influence pulse or blood pressure.
The HealthHub escitalopram guide suggests taking it with or after food for nausea and asking about a different time of day if sleepiness or insomnia is troublesome. For dry mouth it suggests sugar-free gum or sweets and regular sips of water. Report effects that persist, worsen or interfere with daily life.
Its uncommon but serious warnings include bleeding, low sodium, abnormal rhythm, mania and serotonin syndrome. HealthHub describes confusion, muscle weakness or cramps, trouble concentrating and unsteady walking as possible low-sodium symptoms; fainting or a fast or irregular heartbeat can signal a rhythm problem.
Mirtazapine commonly causes drowsiness, increased appetite and weight gain. Those effects may influence selection when sleep or appetite is poor, but can conflict with driving, machinery work or weight and metabolic concerns. HealthHub advises avoiding driving when drowsy and monitoring weight. It also lists rare infection signs, including fever, sore throat and mouth ulcers, associated with bone-marrow suppression and needing immediate medical advice.
With TCAs, dry mouth, constipation, blurred vision and difficulty urinating are among the effects to discuss. Sedation and dizziness on standing matter too. ACE names seizures, arrhythmias and coma among the potentially serious adverse events of first-generation antidepressants, explaining why they are not preferred for routine use. The amount printed in milligrams cannot by itself tell you how safe a medicine is, especially in overdose. A TCA regimen for pain is a separate comparison from treatment for depression.
Which early changes need prompt review?
Seek assessment for new or worsening self-harm thoughts, severe agitation or manic symptoms. Inability to stay safe, markedly reduced need for sleep, unusually elevated or irritable mood, impulsive behaviour, hallucinations and confusion also require prompt attention. Manic or hypomanic symptoms can reveal bipolar depression and change management.
HealthHub highlights behavioural changes particularly in people under 25 and in the first weeks after starting or changing treatment. It says the cause is not always clear. A family member or caregiver can alert the doctor if the person cannot do so themselves.
Suspected overdose, seizure, fainting or a severe reaction needs urgent assessment. Fever with agitation, confusion, heavy sweating and uncontrolled muscle twitching may indicate serotonin syndrome, especially with combined serotonergic medicines or supplements.
ACE advises against combining St John’s wort with antidepressants because of serotonin-syndrome risk. NICE recommendation 1.4.38 also flags interactions with hormonal contraceptives, anticoagulants and anticonvulsants, along with variable preparations and uncertain persistence of effect. Include supplements, traditional remedies and non-prescription products in the medicine review.
Why can stopping feel different from relapse?
Withdrawal often begins within days of reducing or missing treatment. It can cause dizziness, electric-shock-like sensations, nausea, disturbed sleep, vivid dreams, sweating, irritability, anxiety, low mood and flu-like symptoms. SSRIs, SNRIs, TCAs and MAOIs can all cause it. NICE identifies paroxetine and venlafaxine as more likely to be associated with withdrawal symptoms.
In recommendation 1.4.14, NICE gives 1 to 2 weeks as the usual period for withdrawal symptoms to settle. It also describes more difficult withdrawal lasting several weeks, occasionally several months, and sometimes severe symptoms. Relapse does not usually appear as soon as treatment stops. Anxiety and sleep problems can belong to either picture. NICE also cautions that symptoms may take a few days to disappear after restarting. Repeatedly stopping and restarting is not a way to diagnose the problem.
Short half-life medicines need slower tapering, according to ACE; a long treatment history may also call for slower reductions. NICE recommendation 1.4.16 makes the next step depend on symptoms: wait until withdrawal has resolved or is tolerable, at a pace agreed with the patient. At very small amounts, tablets and capsules may not permit gradual enough changes. The guideline suggests a liquid preparation if one is available.
Allow for weeks or months rather than assuming a fixed finish date. The formulation, earlier withdrawal, risk of relapse and urgent adverse effects all affect the plan. NICE describes extra support after a difficult previous attempt, including check-in phone calls, more frequent appointments or sleep-hygiene advice.
What changes the answer?
Diagnosis, safety and previous response guide the choice. Psychosis, bipolar features, severe anxiety, substance use or immediate self-harm risk can require different care. Include falls and effects on driving in the review.
Take a list that includes serotonergic medicines, anticoagulants, NSAIDs, sedatives, stimulants and St John’s wort. Discuss age, pregnancy or breastfeeding and any kidney or liver impairment. For mirtazapine, HealthHub asks specifically about phenylketonuria and an inability to take artificial sweeteners: the orodispersible tablets it describes contain aspartame. These tablets dissolve in the mouth and can be swallowed without water.
Previous benefit or difficult withdrawal is useful history. Pack size and medicine toxicity also matter when there is current or previous self-harm risk.
What should you bring to an antidepressant review?
Bring the packet, dose label, start date and a record of changes. Include missed doses, other medicines and supplements, and changes in mood, sleep, appetite, anxiety, concentration, sexual function and activity. Note what appeared first and whether it followed a treatment change.
In Singapore, call 995 for immediate danger. The national mindline provides 24-hour support on 1771, and Samaritans of Singapore on 1767. The antidepressants category and major-depressive-disorder page explain label terms; the prescriber needs to plan individual treatment and stopping.
Sources
- Singapore Agency for Care Effectiveness: Major depressive disorder: achieving and sustaining remission.
- NICE: Depression in adults: treatment and management.
- HealthHub Singapore: Escitalopram medicine guide.
- HealthHub Singapore: Mirtazapine medicine guide.
- HealthHub MindSG: Preventing self-harm and suicide: helplines.
