Rhubarb is a plant that enjoys cold climates and is found in mountainous and temperate areas of the world like Northeast Asia.

The species Rheum x hybridum is commonly grown as an edible vegetable across Europe and North America.

Although rhubarb is botanically a vegetable, it’s classified as a fruit in the United States (1).

It has long fibrous stalks that range from dark red to pale green. These are often chopped and cooked with sugar due to their very sour taste.

Meanwhile, its large dark green leaves look a bit like spinach and are not usually eaten due to fears about them being poisonous or inedible.

This article provides all the information you need on the safety of rhubarb leaves.

High in oxalic acid

Rhubarb leaves are considered inedible due to their high concentration of oxalic acid. In fact, both the stalks and leaves contain oxalic acid, but the leaves have a much higher content.

Oxalic acid is a natural substance found in many plants, including leafy greens, fruits, vegetables, nuts, seeds, and cocoa (2).

Rhubarb contains approximately 570–1,900 mg of oxalate per 3.5 ounces (100 grams). The leaves contain the most oxalate, comprising 0.5–1.0% of the leaf (3).

Too much oxalate in the body can lead to a condition known as hyperoxaluria, which is when excess oxalate is excreted in the urine. This can also lead to an accumulation of calcium oxalate crystals in the organs (3).

In the kidneys, this can lead to the formation of kidney stones and eventually kidney failure.

Symptoms of mild rhubarb leaf poisoning include vomiting and diarrhea that resolve within a few hours. More serious oxalate toxicity causes sore throat, difficulty swallowing, nausea, vomiting (sometimes including blood), diarrhea, and abdominal pain (3).

Very serious symptoms include kidney failure, numbness, muscle twitches, and cramps.

summary

Rhubarb leaves contain oxalic acid, which can cause build up in the organs and lead to kidney stones and kidney failure when consumed in high amounts. 

Rhubarb leaf poisoning is rare

There are very few reports of either fatal or nonfatal poisoning caused by eating rhubarb leaves.

The reported average lethal dose for oxalate is estimated at 170 mg per pound (375 mg per kg) of body weight, which is approximately 26.3 grams for a 154-pound (70-kg) person (4). 

This means a person would have to eat between 5.7–11.7 pounds (2.6–5.3 kg) of rhubarb leaves for a potentially lethal dose of oxalate, depending on the concentration of oxalate in the leaf. 

However, lethal amounts have also been reported at lower intake levels (2, 5, 6).

During World War I, people were advised to eat rhubarb leaves as a substitute for vegetables that were unavailable at the time, leading to reports of several poisonings and deaths (3). 

There were also reports of poisonings during the 1960s, but because it’s very uncommon to eat rhubarb leaves, there are no reports of deaths from rhubarb leaves in more recent times (5). 

However, there are cases of people developing kidney damage from eating high amounts of rhubarb stems, which also contain oxalic acid (7).  

Additionally, some people are more susceptible to developing kidney stones and kidney damage from oxalates. 

This includes people with certain genetic conditions, as well as those with existing kidney damage, a high vitamin C intake, or vitamin B6 deficiency (7, 8, 9, 10). 

It has also been suggested that both fatal and nonfatal rhubarb leaf poisoning may be caused by another substance known as anthraquinone glycosides — not the oxalic acid. However, more research is needed (3).

summary

Reports of poisoning from eating rhubarb leaves are very rare. A person would need to eat significant amounts of rhubarb leaves to induce symptoms, although some people may be more susceptible to developing kidney problems from oxalates. 

The bottom line

Rhubarb leaves contain high amounts of oxalic acid, which can cause health problems when eaten in higher amounts. 

Symptoms of toxicity include mild gastrointestinal symptoms, as well as more serious problems, such as kidney stones and kidney failure

Although reports of poisoning are rare, it’s best to avoid eating rhubarb leaves, particularly if you have any condition that increases your risk of kidney stones.