What is Can Sha?

Can Sha is the dried droppings of the silkworm, also known as Silkworm Feces. It is a single drug (TCM herb), not a blend or a formula. Herbalists use it mainly for achy, stiff joints and for an upset stomach with vomiting, cramps and loose stools.

Silkworms eat only mulberry leaves, so the droppings are mostly part-digested leaf. The grains are dried, sieved clean, and simmered into a tea. Because the bits float and cloud the water, they are nearly always cooked inside a small cloth bag.

Here is the plain verdict. Can Sha has a long, steady record in Chinese medicine, but we could not find any human trial of it. A long history of use is not proof that something works, and we say that once here rather than at the top of every section below.

How does Can Sha work?

No one has shown how Can Sha works in the body, and the honest answer is that we do not know.

In Chinese medicine terms, Can Sha is said to drive out "wind-damp" from the joints and to settle a churning stomach. That is a traditional way of sorting symptoms, not a description of body chemistry.

Lab work points to the green leaf pigment and other plant leftovers in the droppings. Some of these have calmed swelling in test tubes and in animals. That is a long way from showing an effect in a person.

What forms does Can Sha come in?

Can Sha comes in a few forms. The usual one is loose dried grains, simmered in a cloth bag to make a tea.

- Powder, sometimes packed into capsules. - An ingredient inside ready-made Chinese formulas. - A wash or soak for itchy skin, used on the skin only.

Buy only from a supplier that cleans, dries and tests the material. Never collect or use it yourself from a farm or a hobby setup.

Where it comes from:

Can Sha has been used in China for many hundreds of years and is listed in the classic herb books, including the Ben Cao Gang Mu of 1596.

Its best-known use is in Can Shi Tang, a formula written down by Wang Meng-ying in the 1800s for violent vomiting, diarrhoea and leg cramps.

It is a long-standing staple of one tradition, Chinese medicine. It has no matching record in Western, Ayurvedic or other herb systems.

What does Can Sha help with?

• Aching, stiff joints and muscles: This is the main traditional use, and it rests on tradition alone. Chinese texts use Can Sha for joints that hurt and feel heavy or stiff, often in damp weather. We found no human trial testing it for joint pain. If a joint is hot, red and swollen, get it checked rather than treating it at home.
• Vomiting and diarrhoea with belly cramps: Can Sha is part of the old formula Can Shi Tang, used for sudden vomiting, watery stools and cramping. Again, this is tradition, not trial evidence. Fluid loss is the real danger here. Drink oral rehydration fluid and see a doctor if the vomiting or diarrhoea does not stop.
• Leg and calf cramps: Traditional texts pair cramping legs with the same stomach upset above, and treat both together. No trial has tested Can Sha for cramp. Sudden, hard leg cramps with a lot of fluid loss can mean your salts are low, which is a reason to get help.
• Bloating and a heavy feeling after meals: Chinese practice describes Can Sha as clearing "turbid damp" from the middle of the body, which is the old way of naming this kind of bloating. There is no human research on it. Bloating that keeps coming back, or comes with weight loss, needs a doctor.
• Itchy rashes and hives: Some practitioners boil Can Sha and use the cooled liquid as a skin wash. This use is traditional and small in scale. No trial supports it. Do not use a wash on broken skin, and stop at once if the skin gets redder or more sore.

What are the side effects of Can Sha?

• Upset stomach or loose stools
• Feeling sick (nausea)
• Itchy skin, hives or a rash
• Skin that burns in the sun more easily than usual
• Wheezing, sneezing or a stuffy nose in people allergic to silk or silkworms
• Stomach bugs, if the material was not cleaned and dried well

Good to know:

Side effects seem to be mild and not common. But no one has counted them in a trial, so this is a weak picture.

The two things to watch for are allergy and dirty material. People who react to silk, silk dust or silkworms can react to Can Sha too. And because it is insect waste, poorly handled stock can carry germs.

Stop taking it and get help if your lips or face swell, if your skin breaks out in hives, or if you find it hard to breathe.

How much Can Sha should you take?

• Recommended daily: There is no dose set by modern research. What follows is standard practice in Chinese herbal medicine, not a tested amount. - Tea: 5 g to 15 g of the dried grains a day, simmered in a cloth bag and split into two or three drinks. - Skin wash: made stronger, cooled, and used on the skin only. Do not swallow a skin wash. Start at the low end, and let a trained practitioner set your amount.
• Best time of day: Split the day's amount into two or three warm drinks, spread across the day. Many people take one in the morning and one in the evening.
• With or without food: Take it after food. A full stomach makes mild queasiness less likely. If you are taking any other pills, leave about two hours between them and Can Sha.
• Time to effect: Unknown, since no study has measured this. Traditional use for a stomach upset expects a change within a day or two. For joint aches, practitioners usually look at the one to two week mark.
• How long to take it: Short courses only. For a stomach upset, a few days is normal. For joint aches, most practitioners work in blocks of one to two weeks and then check how you are doing. Stop and rethink if nothing has changed after two weeks. Long, unbroken use has not been studied and is not advised.