What is Hemlock?

Hemlock here means a tree, not the poison. The remedy comes from Abies canadensis, a tree now usually called Tsuga canadensis. It is the eastern hemlock spruce of North America.

Poison hemlock is a completely different plant, Conium maculatum. It is a deadly weed in the carrot family. Never treat the two as the same thing because they share a common name.

American folk healers and Eclectic doctors used two parts of the tree. The inner bark was simmered into a strong, bitter tea. The resin, sold as Canada pitch, was spread on cloth plasters.

Traditional use is not proof that something works, and it is not proof that something is safe. Both have to be shown on their own. For hemlock spruce, neither has been.

The short evidence verdict: no human trials support any medical use of this tree.

How does Hemlock work?

The main proposed action is astringent, meaning it tightens and dries surface tissue. Hemlock bark is rich in tannins. In test tubes, tannins bind to protein and make tissue feel drawn and firm.

That is the basis for the old gargle and skin-wash use. It has not been measured in people with sore throats or wounds.

In laboratory tests, extracts of hemlock bark and needles slow the growth of some bacteria and fungi. Whether this happens in a human mouth or on human skin is not established.

Canada pitch plasters were thought to work by warming the skin. This is a counter-irritant effect, meaning the skin tingles and distracts from deeper aching. No trials have tested this tree for pain.

The needle oil contains bornyl acetate and pinenes. In cell and animal studies these show mild anti-inflammatory activity. That is a long way from a proven effect in a person.

What forms does Hemlock come in?

You will most often meet hemlock spruce in four forms.

Dried cut bark is sold loose for making a tea or a gargle. Liquid extracts and tinctures of the bark are also sold, usually in small dropper bottles.

Canada pitch is the tree resin. It was once a standard plaster base and still turns up in drawing salves and warming ointments.

Needle essential oil is sold for scent and steam. It is strong, and it is meant for the air or for diluted skin use only. It is never swallowed.

Needle tea is a home preparation rather than a product. Quality and strength vary widely between batches, which makes any comparison between products unreliable.

Where it comes from:

Eastern hemlock was a major North American bark tree in the 1800s. Most of it was felled for the tanning trade, not for medicine.

Indigenous peoples of the northeast woodlands used hemlock needle and bark teas as winter drinks. Bark washes were applied to sores and bruises. These were household and community practices, recorded later by outsiders.

Eclectic and folk doctors of the 19th century picked up the same uses. King's American Dispensatory listed the bark as an astringent for throat and bowel complaints.

Canada pitch, listed as Pix canadensis, was an official plaster material in American pharmacy of that era. Its standing came from long habit and from trade supply. None of that was tested the way a medicine is tested now.

What does Hemlock help with?

• Sore throat, as a gargle: This was the most common folk use. The tannin-rich bark tea was gargled to make the throat feel drawn and less raw. No human trial has tested hemlock spruce for sore throat. Any relief may be the warm liquid rather than the plant. A sore throat with high fever, or one lasting more than a few days, needs a doctor, not a gargle.
• Sore or bleeding gums, as a mouth rinse: Eclectic texts recommended the bark tea as a mouthwash for spongy, bleeding gums. Tannins do bind surface protein in test tubes, which is the proposed reason. There is no trial in people with gum disease. Bleeding gums often signal gum infection. That needs a dentist.
• Loose stools and mild diarrhoea: Strong bark teas were taken by mouth for the bowels. Tannins in other plants do have a drying effect on the gut lining. That effect has not been shown for this tree in people. Strong tannin teas also upset the stomach in many users. Diarrhoea with blood, fever, or lasting over two days is a reason to call a doctor.
• Minor cuts, grazes and skin irritation, as a wash: Cooled bark tea was used as a wash for sores and chafed skin. In laboratory tests, bark extracts slow some bacteria. It is not known whether that happens on a real wound. Soap, clean water and a dressing have proven value here. A home brew does not replace them.
• Aching muscles and joints, as a pitch plaster: Canada pitch was spread on cloth and laid over a sore back, chest or joint. It warms and sticks to the skin. The idea was counter-irritation, meaning mild surface tingling that masks deeper ache. No trial has tested hemlock pitch for pain. Resin plasters cause rashes in some people, and the risk rises the longer they stay on.
• Chest congestion, as steam or scent: Needle oil smells sharp and clean, like many conifers. It was used in steam bowls and rubs for stuffy chests. Pine-type oils can make breathing feel easier. That feeling is not the same as clearing an infection, and it has not been measured for this species. Steam and strong conifer oils can trigger wheezing in people with asthma.

What are the side effects of Hemlock?

• Nausea or stomach ache from strong bark tea
• Constipation with repeated use
• Poorer iron absorption from meals
• Dry, puckered feeling in the mouth
• Skin rash or itching from pitch plasters and salves
• Blistering if a plaster is left on too long
• Allergic reaction in people sensitive to conifer resin
• Wheezing or coughing from strong needle oil steam
• Serious poisoning if the essential oil is swallowed

Good to know:

Most reported problems are mild and come from the skin or the stomach.

Rashes from resin plasters are the most common complaint. Stomach upset from strong tannin tea comes next.

The serious risks are different in kind. Swallowing the essential oil can harm the gut, nerves and lungs. Buying a mislabelled product and getting poison hemlock instead is rare but can be fatal.

How much Hemlock should you take?

• Recommended daily: There is no agreed dose for hemlock spruce. No trial has set one, and products differ in strength. Labels on dried bark often suggest about one to two grams steeped in a cup of hot water. Tincture labels often suggest a few drops in water. Those are label figures, not advice for you. The essential oil is not for swallowing at any amount. Plasters and salves carry their own label directions for how much to apply. Ask a pharmacist or doctor before using any form, especially if you take daily medicine.
• Best time of day: Time of day does not matter much for this one. A gargle or mouth rinse is simply used when the throat or mouth is sore. A plaster is usually applied when you can rest. If you take other medicines by mouth, keep the bark tea a couple of hours away from them.
• With or without food: If you take the bark tea or tincture by mouth, food helps. Tannins are harsh on an empty stomach and can cause nausea. Taking it with or just after a meal lowers that chance. One catch: tannins bind iron in food. If you are low in iron, that is a reason to avoid the tea rather than to time it.
• Time to effect: A warm gargle may feel soothing within minutes. That feeling is mostly the warmth and the liquid. A pitch plaster warms the skin within an hour or so. Any easing of ache is short-lived. It is also fair to say it may do nothing at all. No study has shown a real effect in people for any of these uses.
• How long to take it: Short use is the only use tradition describes, and no study backs any length. Gargles and washes were used for a few days at a time. Tannin teas taken by mouth were not meant for weeks on end, because high tannin intake can block iron and upset the gut. If a symptom has not settled within a few days, stop and get it looked at.