The advice that sends people to hospital is “drink plenty of water”
Warning signs
- Headache, nausea, confusion or unusual drowsiness in someone who has been drinking a lot of water — this is the pattern that precedes a hyponatremic seizure, and it looks like nothing at first
- A seizure
- A body temperature you cannot bring down, or skin that has stopped sweating
- Muscle pain and dark urine in the hours or days afterwards
- Chest pain or a heart rate that will not settle
If it goes wrong
- Call emergency services. Say what was taken, how much, when — and critically, HOW MUCH WATER has been drunk. The treatment for too little sodium is the opposite of the treatment for dehydration, and a clinician who is not told will reasonably assume the wrong one.
- For overheating: get the person somewhere cool, stop the dancing, remove layers. Do not force fluids to fix a temperature.
- Stay with them. The literature's own case was a witnessed seizure in someone with no medical history at all.
Legal framework
| ES | Consumption or unlawful possession of controlled substances in public places, roads, public establishments or public transport — even when not intended for trafficking — is a serious administrative offence under the citizen-security law. Trafficking is a separate criminal matter. This describes the public-place case only; it is not a statement that possession is lawful. as of 2026-07-18 · Ley Orgánica 4/2015, de protección de la seguridad ciudadana, art. 36 (BOE-A-2015-3442) |
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| IE | MDMA is listed in Schedule I of the United Nations 1971 Convention on Psychotropic Substances and is under international control; signatory states prohibit it. This entry stands for the international baseline — the floor, not the whole story. Your own country's current text is the one that applies to you. as of 2026-07-18 · European Union Drugs Agency (EUDA/EMCDDA), MDMA drug profile — control status |
This describes the law as of the date shown; it is not legal advice. The law changes and differs by country — checking yours is your responsibility.
Dangerous interactions
water, drunk on the standard advice life-threatening
This is the interaction almost nobody names, and it is the one in the case literature. MDMA is associated with a state of inappropriate antidiuretic hormone production: the body stops shedding water at the same time as heat and dry mouth drive the person to drink more. A review of MDMA-induced hyponatremia describes a 29-year-old with no past medical history brought in after a generalised tonic-clonic seizure with a serum sodium of 117 mMol/L against a reference range of 136–146. The review states plainly that a falsely safe drug profile coupled with a misconception about water intake has left many unaware of these complications. The water is not the antidote here — past a point it is the injury.
MDMA-Induced Hyponatremia: Case Report and Literature Review (PMC8232921)
heat, crowds and hours of dancing serious
The same review lists hyperthermia among the acute toxicities alongside agitation, acute liver toxicity, fulminant liver failure, rhabdomyolysis and disseminated intravascular thrombosis — and notes that serotonin release affects the body's temperature regulation, which in turn drives the excessive thirst that starts the water problem. Heat and hydration are not two separate risks here; they are one loop feeding itself.
MDMA-Induced Hyponatremia: Case Report and Literature Review (PMC8232921)
What the sources report
| oral | The EU drugs agency does not publish a recreational range, and neither will we. What it does report: after a dose of 75 mg the peak plasma concentration of around 0.13 mg/L is reached within two hours, and fatalities following a dose of 300 mg have been noted — with the explicit caveat that toxicity depends on many factors, including individual susceptibility and the circumstances of use. Peak plasma concentration is reached within about two hours of a 75 mg dose. The plasma half-life is 6–7 hours, so the drug is still in the body long after the experience feels finished. European Union Drugs Agency (EUDA/EMCDDA), MDMA drug profile |
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Almost every piece of advice about this substance ends with "and drink plenty of water". It is repeated by people who mean well, and it is how a 29-year-old with no medical history ends up in an emergency department after a generalised seizure, with a serum sodium of 117 against a normal range of 136 to 146.
Why the water turns
Two things happen at once. MDMA is associated with a state in which the body holds on to water instead of shedding it. And the heat, the dancing and a dry mouth make a person want to drink far more than usual.
Hold water in, pour water on top. The sodium in the blood drops, the brain swells, and the first outward sign of it can be a seizure in someone who felt fine an hour earlier. The review that documents this says the quiet part directly: a falsely safe reputation, combined with a misconception about water intake, has left many people unaware of exactly this.
That is what makes it worth a page. Not the substance's danger in the abstract — the fact that the most repeated safety advice about it is, past a point, the mechanism of the injury.
What the numbers actually say, and what they do not
The EU agency does not publish a recreational dose range for MDMA, and this page will not invent one. What it publishes is pharmacokinetics: 75 mg produces a peak plasma concentration of about 0.13 mg/L within two hours, and the plasma half-life is 6 to 7 hours.
That half-life is the useful number. It means the drug is still measurably present long after the experience feels over — which is the window in which people redose, drink more, and stay in the heat because the night is not finished.
It also notes that fatalities following a 300 mg dose have been recorded, immediately qualified: toxicity depends on many factors, including individual susceptibility and the circumstances of use. Read the qualifier, not just the number. There is no dose here that a stranger can certify as safe for you, and this page is not going to pretend otherwise.
The sentence that matters at the hospital door
If someone is taken to hospital, say how much water they have drunk.
Low sodium and dehydration look similar from the outside and are treated in opposite directions. A clinician who is not told about the litres will reasonably reach for fluids — and that is the one thing that must not happen if the problem is dilution. It costs you a sentence.
The honest summary
The heat and the water are the same problem wearing two faces, and the standard advice only addresses one of them.
Sources
- European Union Drugs Agency (EUDA/EMCDDA), MDMA drug profile (retrieved 2026-07-18)
- MDMA-Induced Hyponatremia: Case Report and Literature Review (PMC8232921) (retrieved 2026-07-18)
- Ley Orgánica 4/2015 de protección de la seguridad ciudadana (BOE-A-2015-3442) (retrieved 2026-07-18)