Prodrome is the early-warning phase of a migraine attack — the period 2 to 48 hours before head pain begins, during which the brain is already operating in migraine mode but you don’t have a headache yet. It is also called the premonitory phase.
Roughly 60–70 percent of people with migraine report at least one recognisable prodromal symptom; the rest either don’t get one or don’t recognise it. The phase is biologically real — multiple hypothalamic and brainstem changes are measurable hours before pain onset — but the symptom experience varies enormously between individuals.
What prodrome looks like
The most commonly reported prodromal symptoms, in rough order of frequency:
- Fatigue and tiredness — a heavier, unusual flatness, not just end-of-day tiredness.
- Yawning — repeated, unusual yawning unrelated to sleep.
- Mood change — irritability, anxiety, or sometimes a brief euphoria.
- Food cravings — often salt or specific carbohydrates.
- Neck stiffness or pain — frequently misread as the cause of the migraine rather than a precursor.
- Frequent urination — driven by hypothalamic changes.
- Light or sound sensitivity that’s milder than the full attack but already present.
- Difficulty concentrating or word-finding lapses.
Two important notes:
- Symptoms are personal. Most people who experience prodrome have a small consistent set — maybe two or three of these — that recur attack-to-attack. The full list is the population composite, not what any one person should expect.
- Tracking helps spot it. Many people only realise they had a prodromal phase after the fact, when reviewing logs. A forecast app or paper diary that records mood, energy, and sleep can surface a pattern that was invisible day-to-day.
Prodrome vs aura — they are not the same
The two are often conflated, but they’re different phases:
| Feature | Prodrome | Aura |
|---|---|---|
| Timing | 2–48 h before headache | 5–60 min immediately before / during |
| Duration | Hours, sometimes days | Minutes |
| Symptoms | Systemic (fatigue, mood, cravings) | Neurological (visual, sensory, language) |
| Prevalence | ~60–70% of people with migraine | ~25–30% |
| Treatable window | Possibly, with acute meds (per PRODROME trial 2023) | Generally too short to abort |
Aura — flashing lights, zigzag patterns, numbness in one hand — is a different neurological event with a different mechanism (cortical spreading depression). It’s also the basis for the ICHD-3 distinction between “migraine with aura” and “migraine without aura”.
What Hermly forecasts (and what it doesn’t)
Hermly does not detect prodromal symptoms automatically — there is no objective biomarker for prodrome that a phone or Apple Watch can read. What Hermly forecasts is the 24-hour risk of an attack starting, based on physiological signals (sleep, HRV, cycle, weather, recent attack history) that often shift during the prodromal window even when you don’t consciously notice them.
This is why a high Hermly forecast at 8 AM can sometimes feel unexpected — you don’t have any subjective warning yet, but your overnight HRV dropped and your pressure forecast shows a 12 hPa drop. The model is, in effect, doing pattern recognition on the physiology of the prodromal window without needing you to label your own symptoms.
The opposite case also happens: you can feel a clear prodromal symptom (the unmistakable craving, the strange yawning) on a day the model rates “Low”. That’s the model telling you it doesn’t see the physiological signal — not that the prodrome isn’t real. Your subjective experience is the ground truth for your attacks. The model is a supplementary read.
Acting on a prodrome
The 2023 PRODROME trial (published in Lancet) found that some preventive medications taken during a recognised prodromal phase reduced the likelihood of progression to full headache. Whether that’s appropriate for you is a medical decision — it depends on your specific medication, attack frequency, and overall plan.
Hermly does not recommend medication and does not prompt you to take any. What it does is make the risk window legible, so you and your doctor can decide together what to do with that information.
Related Hermly product behaviour
When today’s risk is high and you’ve previously logged frequent prodromal symptoms, the Today screen surfaces three factors that moved the score (e.g., “Sleep below baseline · Pressure dropping · Cycle day 27”). It does not tell you you’re in a prodrome — because we can’t know that. It tells you what the model saw.