A poison is any substance which has a harmful effect on a living
system. Paracelsus (1493-1541) was one of the first to distinguish
between the therapeutic and toxic properties of substances. He taught
that the only difference between a medicine and a poison was the dose.
Very few substances are actually classed as a "poison". Harmful
chemicals are not necessarily poisons. We are exposed to potentially
toxic substances every day without immediate harm. Our bodies can
usually safely metabolize toxins if we are exposed to them in small
amounts. It is only when we overwhelm our body and reach the toxic dose
of a substance that life-threatening results occur.
That is, all substances have a potential toxicity. All herbs can
therefore be harmful, but most would have to be ingested in impossible
amounts to cause harm. Herbs which have a high toxicity, such as
Gelsemium and Aconitum, can be used safely and effectively if taken in
a small, therapeutic dose. Thus, the primarily determinate of the
safety of a substance is the dose. It is the dose, not the herb, which
makes the poison. A correct use of semantics and a correct
understanding of these terms is crucial to avoid confusion and
misinformation.
For example:
- Vitamin D has a very high acute toxicity. It would have had to carry
a poison label but it has been exempted from the Federal Hazardous
Substances Labeling Act because it is classed as a food and a drug.
- Salt is not toxic in small doses. But a single large dose can be
lethal. Just two tablespoons can kill a one-year-old child.
- Caffeine, one of the many alkaloids found in coffee can kill - at a
dose of 100 strong cups of coffee.
- A liter of scotch contains a lethal dose of ethanol.
- Water can be lethal if you drink enough of it in a short period of
time.
Toxicology sometimes refers to potentially poisonous substances as
xenobiotics after the Greek xenos, strange, and bios, life. These are
substances that are foreign to the body or exogenous as compared to
substances produced by the body or endogenous. It is important to point
out that endogenous substances can also cause poisoning and death.
Toxic substances fall into several classes in relation to how people
are exposed to them. They can be classed as: food additives, drugs,
pesticides, industrial chemicals, environmental pollutants, household
poisons, and natural toxins. Many natural products used in medicine are
derived not only from plants, but also from marine organisms like
starfishes, sea urchins, sea cucumbers and fish. Chinese medicine makes
use of chemicals produced from animals such as antelope horn, worms,
scorpions and bee hives.
Every substance has potential toxicity, from the most benign to the
most obvious. Even so, the same dose will not affect every person in
the same way. It is this fact which makes toxicology such a complex
science. It is not enough to say a substance is toxic. There are a
myriad of factors which may make the substance more or less toxic to a
particular individual.
