What is Astacus fluviatilis?

Astacus fluviatilis is a homeopathic remedy. It is made from the European crayfish, a small freshwater shellfish. In homeopathy it is used mainly for itchy skin rashes, above all hives (raised itchy welts).

Like all homeopathic remedies, it is watered down again and again in a set way. This is called serial dilution. At 30C the source has been thinned so far that no crayfish is likely to be left in the pill at all.

Trials have not shown homeopathic pills to work better than a dummy pill. Long use in one tradition is not proof that a remedy works. Both things are true at once, and this page reports both.

How does Astacus fluviatilis work?

There is no known way this remedy could act on the body once it is diluted to 30C. Nothing of the crayfish is left to act.

Homeopaths work from an old idea called "like cures like". They say a thing that causes a rash in a well person can, when watered down, help a sick person with a like rash. They also say the shaking step at each dilution leaves an imprint in the water.

Chemistry and biology do not support that idea. When people feel better after taking it, the likely reasons are placebo effect (feeling better because you expect to), time, and the fact that hives often clear on their own.

What forms does Astacus fluviatilis come in?

You will most often see:

Small sugar pellets or pills, sold as 6C, 30C or 200C. Liquid drops in a water and alcohol base. Tablets that melt under the tongue.

The mother tincture and very low strengths, such as 1X to 6X, are rare and are the only forms that may still hold crayfish protein. These are the forms that matter if you have a shellfish allergy.

Where it comes from:

Astacus fluviatilis entered homeopathy in the 1800s in Europe. It is a small, minor remedy, not a famous one.

Old homeopathic texts, such as the materia medica collections of the period, list it for nettle rash that comes with fever, chill or liver complaints. It has stayed a minor entry in that one tradition ever since, and it has no separate record in herbal medicine, Ayurveda or Chinese medicine.

What does Astacus fluviatilis help with?

• Hives (raised itchy welts on the skin): This is the main use in old homeopathic books. No human trial has tested the remedy for hives. Hives often settle on their own within days, which makes any home remedy look helpful. If hives keep coming back for six weeks or more, see a doctor to find the cause.
• Itchy rash that flares when you uncover the skin: Homeopaths pick remedies by small details like this one. The detail comes from old case notes, not from testing. There is no trial evidence behind it.
• Nettle rash that comes on with fever or chill: Old texts link the remedy to a rash that shows up with a fever. A rash with a fever can be a sign of an infection that needs real care. Get this checked by a doctor rather than treating it at home.
• Skin rash blamed on a sluggish liver in old texts: Writers in the 1800s tied itchy skin to the liver. That link is not how doctors understand liver disease today. There is no evidence this remedy helps the liver in any way.
• Swollen glands in the neck with a rash: This is listed in the old picture of the remedy. It has never been tested in people. Swollen glands that last more than two weeks need a doctor, not a home remedy.

Which foods are rich in Astacus fluviatilis?

1. Crayfish: the source animal, eaten in many parts of Europe
2. Shrimp, crab and lobster: close relatives, and the same allergy risk

What are the side effects of Astacus fluviatilis?

• Allergic reaction if you are allergic to shellfish and take the mother tincture or a very low strength such as 1X to 6X
• A short flare of the rash or itch in the first day, which homeopaths call an aggravation
• No change at all
• Upset stomach or wind in people who cannot digest lactose (milk sugar), from the pill base
• Sore mouth or mild burning from the alcohol in liquid drops
• Harm from waiting too long before getting real care

Good to know:

Side effects from 30C pills are rare. At that strength the pill is sugar, so there is little in it that can harm you.

The two real risks are different. One is a shellfish allergy plus a low-strength product that still holds crayfish protein. The other is using this instead of care that works, while a rash, a fever or a swelling gets worse.

How much Astacus fluviatilis should you take?

• Recommended daily: There is no proven dose, because the remedy has not been shown to do anything. Shop labels for 30C pills usually say 3 to 5 pellets, two or three times a day. Let them melt under the tongue. Follow the label on the pack you buy, and treat those numbers as custom, not as a tested dose.
• Best time of day: Any time of day. Homeopathic custom says to keep the mouth clear of food, drink, mint and strong smells for about 15 minutes either side of a dose.
• With or without food: Between meals, on a clear mouth, is the usual custom. Food does not change how the remedy works, since there is nothing in it to absorb.
• Time to effect: No effect can be promised. People who report relief usually say it came within hours to a day or two, which is also how long hives often take to fade by themselves.
• How long to take it: Short-term use only. If a rash has not eased in two or three days, stop and get it looked at. Do not keep taking it week after week for a problem that is not getting better. That delay is the real risk with this remedy.