Side effects that usually ease in the first weeks
These are the effects most people encounter early on. For the majority, they settle meaningfully by week three.
Nausea. Most often in the first one to two weeks; typically softens by week three. Taking the dose with food is recommended in TGA and FDA product information for many medications.
Headache. Most common in week one; usually softens by week two.
Light-headedness. Most common in the first week and after dose changes. Persistent light-headedness — beyond the first week or after dose stabilisation — warrants prescriber review.
Sleep changes. Broken sleep, vivid dreams, earlier waking. Documented as a class effect of many antidepressants; typically ease meaningfully by week three.
Restless or jittery feeling. Common in week one; typically fades. Caffeine reduction often helps in clinical and patient-resource guidance.
Temporary increase in anxiety. Well-documented in the first one to two weeks, particularly for SSRIs; usually settles by week three. See the article on why anxiety can increase early on.
Side effects worth raising with your prescriber
These are not necessarily emergencies, but are conversations to have sooner rather than later. They are documented in major prescribing resources and routinely discussed in informed-consent conversations.
Emotional blunting that is significant or persistent. Discussed in Maudsley Prescribing Guidelines and Royal College of Psychiatrists resources.
Sexual side effects — common, often under-discussed in primary care, and routinely listed in TGA and FDA product information.
Significant weight change in either direction over months.
Persistent sweating or night sweats.
Jaw clenching or teeth grinding.
Side effects affecting work, sleep, or eating beyond week three.
Side effects to flag immediately
Contact your prescriber or seek help immediately
- New or worsening suicidal thoughts — do not wait for a scheduled appointment.
- Severe agitation, confusion, or unusual neurological symptoms — tremor, fever, racing heart, or marked sweating occurring together.
- Allergic-type reactions — rash, swelling, or changes in breathing.
What the evidence says about prevalence
Prevalence of specific side effects is heavily medication-dependent and is documented in TGA and FDA product information for each medication. Across major SSRI and SNRI classes, side effects affecting roughly one in five to one in three patients in the early weeks are common — the precise figure varies by medication and study. Most clinically significant side effects are listed in patient information leaflets dispensed with the prescription, which are an authoritative source for your specific medication.
A practical principle the literature supports
Track what you notice
Patient self-tracking is endorsed in NICE, RANZCP, and Royal College of Psychiatrists patient resources as a useful adjunct to follow-up care. "Nausea in the mornings of the first week, gone by week three" or "jaw clenching started in week two and is still there at week four" is more useful at the next appointment than memory alone.
Frequently asked questions
What are the most common side effects of starting an antidepressant?
Across major prescribing resources, the most consistently reported early effects are nausea, headache, sleep changes, restlessness, and a transient increase in anxiety. Most ease by week three for the majority of patients.
Which side effects mean I should stop the medication?
Decisions to stop or change an antidepressant should be made with your prescriber, not on your own — abrupt stopping can produce discontinuation symptoms. Side effects warranting an immediate conversation include new suicidal thoughts, severe agitation, allergic reactions, or any new neurological symptoms.
How long do side effects last on average?
Most early physical side effects ease meaningfully by the third week according to consistent descriptions in NICE, RANZCP, and Royal College of Psychiatrists resources. Some side effects — emotional blunting, sexual side effects — can persist for the duration of treatment for a subset of patients, and are worth raising with your prescriber if they do.
Related articles
Evidence and sources referenced
- TGA — Australian product information for SSRI and SNRI classes.
- FDA — US prescribing information for SSRI and SNRI classes.
- NPS MedicineWise — patient resources on antidepressant side effects (Australia).
- NICE Guideline NG222 — Depression in adults: treatment and management.
- RANZCP — Clinical Practice Guidelines for Mood Disorders.
- Royal College of Psychiatrists — patient information on antidepressants.
- Maudsley Prescribing Guidelines in Psychiatry — comparative side-effect profiles.
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