Educational information, not medical advice — ask your doctor or midwife.
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Mercurius cyanatus is a single homeopathic remedy. It is made from mercuric cyanide, a very poisonous mercury salt. Its Latin name is Hydrargyri cyanidum.
Homeopaths have used it for sudden, severe sore throats. The old case notes describe a grey or dirty film in the throat, great weakness, and a foul smell. That picture matches diphtheria, a dangerous throat infection.
The remedy is made by diluting the poison again and again, with shaking at each step. At 30C there is essentially none of the starting material left. Trials do not show it works better than a dummy pill (placebo), so long use in homeopathy is not proof that it works.
This page tells you what tradition claims and what the evidence shows. A severe sore throat with fever or trouble breathing is a medical emergency. It needs a doctor, not a remedy.
There is no accepted way for this remedy to act in the body, because at common strengths there is nothing of the source left to act.
Homeopathy works on its own idea, called "like cures like". Raw mercuric cyanide burns and ulcers the mouth and throat. So homeopaths give it, in tiny dilutions, for illness that looks the same.
Homeopaths also say the water and alcohol keep a "memory" of the poison after shaking. Chemistry and physics give no support for this idea. No test has shown a difference between a 30C pill and a plain sugar pill.
Any benefit people notice is best explained by placebo effect, by careful listening from the practitioner, and by the fact that many mild throat infections settle on their own.
It comes as tiny sugar pellets, larger round pills, or liquid drops in alcohol. Strengths sold most often are 6C, 12C, 30C and 200C.
The C scale means one part in a hundred, repeated. The X scale means one part in ten, repeated. So 30C is far more dilute than 6X.
Low strengths such as 3X or 6X may still hold traces of the raw poison. Stick to high dilutions and buy from a known, licensed maker. Never handle or take raw mercuric cyanide in any form.
Mercuric cyanide came into homeopathy in the 1800s. Homeopaths took small doses, wrote down what they felt, and built a symptom picture from it.
It became known as a throat remedy in the years before antibiotics and the diphtheria vaccine. Old case books praise it for ulcerated, foul-smelling throats.
It still appears in homeopathic reference books today. Its standing rests on those old notes and on practice habit, not on modern testing.
Some reactions to Mercurius cyanatus need urgent care. Call your local emergency number or go to an emergency department straight away — do not wait to see whether it passes.
Get emergency help straight away if there is trouble breathing, noisy or squeaky breathing, drooling, a swollen neck, a grey film in the throat, or if the person is floppy, confused or hard to wake.
See a doctor the same day for a fever above 38.5C, a rash with a sore throat, pain that makes swallowing impossible, or a sore throat in someone with a weak immune system.
See a doctor soon if a sore throat lasts more than a week, if a mouth ulcer lasts more than three weeks, or if symptoms return again and again.
If you have swallowed raw mercuric cyanide, or think a child has, treat it as poisoning and call emergency services at once.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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