Herb Info - Safety Ratings

by Anthony Thompson

This post is information that will support future posts on specific herbs. One problem with most information I find about herbs is that there is little relevant discussion on the safety of herbs. Most web sites, blogs or books talk a lot about the benefits of herbs or about the possible dangers of herbs but none of this discussion is framed in a context that gives consumers an easy way to compare various claims. While therapeutic effectiveness and dangerous side effects are important, there is a way that we can look at the safety of different herbs in relation to each other and in relation to other substances, including pharmaceuticals. There is an internationally recognized system of testing for toxicity (hence relative safety) of any substance. This system is called LD50 testing.

LD50 Testing

LD50 is a form of testing, usually performed on rats or mice, that determines the relative toxicity of a substance. The animals are given varying high doses of the test substance. The LD50 level is the dose that is lethal for 50% of the population. (Wikipedia 2009) Though this is certainly cruel for the rats and mice, it provides researchers with a valuable tool. They can look at these numbers and see how toxic different substances are in relation to each other. We can use these same numbers to compare the safety of various herbs in relation to each other and other substances.

A Relative Safety Rating

I am going to use these numbers to set up a rating system in simple English to show how safe substances are relative to all others. First, let's look at some of the details. An LD50 rating is expressed as number of grams or milligrams per kilogram. This is the dosage amount of a substance required per kilogram of body weight to produce death in 50% of the population. Here's an example; caffeine when tested in rats has LD50 rating of 192 mg/kg. (Wikipedia 2009) That means that if you give a dose of 192 mg/kg of caffeine to any population of rats, half (50%) will die. So how do we translate these numbers into a meaningful rating system, below I have broken down the LD50 ratings into five broad categories with a descriptive title for its relative safety.

1. Safest - these substances have an LD50 of greater than 10,000 mg/kg (10g/kg). In this category are water, table sugar and vitamin C. It would be very difficult to maintain doses high enough to be lethal with these substances. It is possible but highly improbable because most of these substances can be quickly broken down and excreted from the body.
2. Safe with proper use - these substances have an LD50 of greater than 500 mg/kg (0.5 g/kg) but less than 10,000 mg/kg (10/kg). Ethanol (grain alcohol), table salt, many pharmaceuticals and most medicinal herbs fall into this category. With these substances you need to know what dosage is safe and stick to it. If you are not sure what is safe, consult a professional.
3. Safe with supervision - these substances have an LD50 of greater than 100 mg/kg (0.1 g/kg) but less than 500 mg/kg (0.5g/kg). These are generally pharmaceutical substances that require a prescription. You will want professional supervision to determine dosing.
4. Dangerous - these substances have an LD50 rating of greater than 1 mg/kg (0.001 g/kg) but less than 100 mg/kg (0.1 g/kg). Many of these are poisons but some pharmaceutical drugs also fall into this category. They should only ever be used under strict supervision.
5. Extremely dangerous - these substances have an LD50 of less than 1 mg/kg (0.001 g/kg). Most of us will never have access to anything this toxic. These substances are strictly regulated in most countries. The one that everyone seems to know these days is Botulinum toxin (Botox), which is so toxic that its LD50 level can only be estimated. (Wikipedia 2009)

This rating will appear only to give readers a general idea of the safety of a particular herb. There are, of course, specific safety considerations for each herb that should also be taken into account. Examples are possible drug interactions and possible side effects of the herbs themselves. These must be weighed along with the relative safety rating when considering if an herb might be helpful for you.

Source
Median Lethal Dose. Wikipedia web site (English version): 2009. Available at: http://en.wikipedia.org/wiki/LD50. accessed April 24, 2009.