Week by week
Across guidance from NICE, RANZCP, and NPS MedicineWise, the first week is characterised by physical side effects — most commonly nausea, headache, sleep disruption, and a transient increase in anxiety for some people. Mood is typically unchanged. Major prescribing resources recommend taking the dose at the same time daily, with food where tolerated, and keeping a simple record of how you feel.
Week two is one of the highest-risk windows for early discontinuation, documented in multiple population studies and Cochrane adherence reviews. Early side effects may still be present, the mood benefit has typically not yet arrived, and the novelty of starting treatment has worn off. This is precisely when major guidelines (RANZCP, NICE) recommend the first follow-up appointment — usually within one to two weeks of initiation — to support adherence through this period.
By the third week, most early physical side effects ease meaningfully for the majority of patients, according to clinical descriptions in NICE NG222 and RANZCP Mood Disorders guidelines. Sleep often improves; nausea has typically resolved; the wired or jittery feeling, where present, usually fades. Mood is still often unchanged at this point. If side effects are easing and mood has not yet shifted, this is on the typical trajectory described in the literature.
RANZCP, NICE, and Maudsley Prescribing Guidelines consistently describe weeks four to six as the window when the first measurable mood improvement typically appears for those who will respond. The change tends to be subtle: less reactivity, quieter background anxiety, slightly more capacity for things that had felt difficult. If no meaningful change has occurred by week six to eight, NICE specifically recommends a review with the prescriber to consider dose adjustment, augmentation, or switching.
What the evidence shows about response patterns
Across major guidelines, full antidepressant response is typically described as taking between four and twelve weeks. Cochrane reviews of antidepressant efficacy report meaningful effect sizes by weeks six to eight at an adequate dose, with continued improvement for many patients out to twelve weeks and beyond. Early response within two weeks is documented for a subset of patients but is not the norm — absence of response in the first three weeks is not evidence the medication will not work.
What to flag to your prescriber
- New or worsening suicidal thoughts — contact your prescriber or emergency services immediately
- A sustained spike in anxiety or agitation that is not settling through the first weeks
- Side effects that are stopping you from sleeping, eating, or functioning — not just uncomfortable, but significantly disruptive
- Any unusual neurological symptoms — confusion, tremor, fever, or a racing heart that is not normal for you
Do not wait for the scheduled appointment. These are exactly the situations every major guideline body says prescribers want to hear about early.
Frequently asked questions
Why are weeks two and three the hardest?+
Side effects are often still present, the mood benefit has not yet arrived, and the early commitment to starting has faded. Multiple Cochrane reviews of adherence identify this window as the highest-risk period for stopping treatment without prescriber knowledge.
What if I have no improvement at all by week four?+
Major guidelines including NICE NG222 and RANZCP describe weeks four to six as the typical window for first response. No change at all by week six is the point at which most guidelines recommend a review to consider dose, switch, or augmentation — not earlier, but not later either.
Are dose adjustments common in the first month?+
Yes. NICE, RANZCP, and Maudsley Prescribing Guidelines describe a starting dose followed by titration upward as common practice, particularly where the starting dose was deliberately low to manage early side effects. Dose changes are typically discussed at the first follow-up appointment.
Evidence and sources referenced
- NICE Guideline NG222 — Depression in adults: treatment and management (United Kingdom)
- RANZCP — Clinical Practice Guidelines for Mood Disorders
- NPS MedicineWise — prescriber and patient resources on antidepressant initiation
- Royal College of Psychiatrists — patient information on antidepressants
- Cochrane Library — antidepressant efficacy and adherence reviews
- Maudsley Prescribing Guidelines in Psychiatry — dose titration and response timelines
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