Dehydration and migraine

What studies show

The evidence is thin, and hydration is rarely measured directly. A 2021 narrative review concluded that dehydration alone may cause headache but often worsens an underlying condition such as a primary headache disorder (Arca 2021).

Study	Design	People	Result
Blau 2004	Case series from family, colleagues and acquaintances	34 people	Headache after water deprivation. Drinking relieved it within 30 minutes in 22 and within 1 to 3 hours in 11
Spigt 2005	Pilot randomised trial, 1.5 L extra water a day	Not given in the review	Fewer headache hours and attacks, but not statistically significant
Spigt 2012	Randomised trial in primary care, 3 months, 1.5 L extra water a day	102 with recurrent headaches, drinking under 2.5 L a day	Migraine-specific quality of life up 4.5 points (95% CI 1.3 to 7.8). 47% reported much improvement vs 25% of controls. No clinically relevant change in days with moderate headache
Khorsha 2020	Cross-sectional	256 women with migraine	Drinking about 2 L a day linked to lower severity, duration and frequency

The Spigt 2005 and Khorsha results are as reported in Arca 2021.

Water-deprivation headache has been proposed as a diagnosis but is not in ICHD-3 (Arca 2021).

Limits of this evidence

• The main trial was weak. A critical appraisal called it underpowered, with partial unblinding and significant attrition. Only subjective measures reached significance (Price 2015). Participants had recurrent headaches, not only migraine.
• Cross-sectional data show no direction. Women who drink more may differ in other ways.
• Fasting studies are confounded. Migraine days rose during Ramadan, but fluid and caffeine intake were not recorded, and food intake changed at the same time (Abu-Salameh 2010).

Fluid advice differs. The American Migraine Foundation mentions two litres a day, and the Migraine Trust six to eight cups or glasses. Neither figure was tested as a migraine treatment in the studies above.

Mechanism

Not established. The review states that the pathophysiology is not fully understood. One suggestion is stretching of the dural veins, and the review describes the mechanism as probably variable and multifactorial (Arca 2021).

Thirst as an early symptom

The Migraine Trust lists feeling thirsty and passing more urine among prodrome symptoms, which can start hours or days before an attack. Thirst the evening before an attack may therefore be part of the attack, not proof that you were short of fluid. Vomiting during an attack also causes fluid loss, so dehydration afterwards does not show the cause.

How to check it in your diary

1. Record what happened, not only how you felt: long gaps without drinking, heat, exercise, illness. The American Migraine Foundation notes that heat and humidity can also cause dehydration, so the weather needs its own entry.
2. Keep thirst as a separate entry with a time.
3. Note alcohol. Alcohol has its own evidence, and the two are easy to confuse.
4. Count dry days with no attack.

For the general method, see how to test a suspected trigger. The printable diary has a column for possible triggers.