Science Questions with Surprising Answers
Answers provided by
Dr. Christopher S. Baird

Are any pills perfectly safe?

Category: Health      Published: December 15, 2014

By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and Associate Professor of Physics at West Texas A&M University

bottle of pills
Public Domain Image, source: Christopher S. Baird.

Nothing in this world is perfectly safe. Even drinking too much water can kill you. Newspapers contain several sad accounts of people dying of water overdose, many of them a result of drinking competitions, extreme child discipline, or fad diets. For instance, Jennete Killpack was sent to prison for killing her daughter by forcing her to drink large amounts of water as a punishment. In a separate case, Jennifer Strange died of water overdose while participating in a water drinking contest sponsored by a local radio station. Drinking high levels of water leads to a potentially lethal condition known as "water intoxication" or "dilutional hyponatremia". In this condition, the excess water dilutes the sodium in the body down to dangerously low concentrations, leading the brain to take up water and swell to the point of failure. In this way, even a substance that is considered one of the least toxic in the world can kill you. The same concept applies to everything we eat, drink, breath, and touch. Even the oxygen we breath, which is essential to life, can cause intoxication and death when breathed at high pressure.

My point is not to scare you into being afraid of everything around you. My point is to show that requiring a pill to be perfectly safe before ingesting it is pointless, since nothing is perfectly safe. A better approach is to choose the pill, food, or drink that is the safest choice. Drinking too much water may kill you, but drinking no water at all will also kill you. The safest alternative is to drink a moderate amount of water. Although "perfectly safe" does not exist, some options are typically "relatively safe" compared to the other options. The best approach is to choose the course of action which maximizes the long-term benefits while minimizing the long-term risks. For example, a pregnant woman with uncontrollable vomiting (hyperemesis gravidarum, which is different and more severe than morning sickness) is faced with the choice of taking antiemetic medication such as promethazine. While taking antiemetic medication carries certain risks, not taking the medicine carries an even greater and very real risk of dying of dehydration from all of the vomiting (the author Charlotte Bronte is believed to have died of dehydration caused by hyperemesis gravidarum). In this case, the course of action with the least risk and the most benefit is typically taking the antiemetics. In contrast, a pregnant woman that only has standard morning sickness is not at risk of dying from dehydration. For such women, taking the antiemetics becomes the riskiest course of action and gives little long-term benefit. For this reason, doctors do not usually prescribe antiemetics to women with standard morning sickness.

As should be obvious at this point, you can't label some substances as always safe, and other substances as always dangerous. The situation is more complicated than that. In general, there are several factors that determine the risk that a substance can harm a person:

1. The toxicity of the substance
This is a measure of how much damage a standard amount of substance can cause. Water has a very low toxicity, caffeine has medium toxicity, and arsenic has high toxicity. This quality is innate to the chemical properties of the substance. Because of their high risk even when in small amounts, high-toxicity substances are typically regulated, handled, and administered by trained professionals.

2. The dose of the substance
This is a measure of the total amount of the substance that the person ingests or is exposed to. The safety of a substance is highly dependent on the dose. Drinking a cup of pure household bleach will do significant damage, but adding a teaspoon of bleach to 5 gallons of water can help make the water safer to drink. High doses of morphine can cause abnormal mind states and suppressed breathing, but the small amount of morphine found naturally in poppy seeds will have very little effect. A few bites of licorice candy are harmless, but eating several bags of licorice can give you high enough blood pressure to land you in the hospital. For substances that the body does not require in order to function normally, the safest dose is typically the lowest dose possible that can be practically achieved. A chemical can't hurt you if you are never exposed to it in significant quantities. For substances that the body needs, the situation is more complicated. Too little of the substance and your body will be malnourished or untreated. Too much of the substance and the toxic effects become significant. Therefore, for substances such as oxygen, water, food, vitamins, dietary elements, and medications necessary to treat disease, there is an ideal dose somewhere in the middle between zero and fatally toxic. How can you know what the ideal dosage is? For simple nutrients, our bodies have built-in feedback mechanisms. If you are drinking too little water, you feel thirsty. If you are drinking too much water, you feel nauseated. As long as you listen to your body (and have no underlying disease), there is little chance of you dying from dehydration or water intoxication. For medications, the situation is more complex since the body does not always have natural mechanisms to tell you that you are getting too much or too little of the medication. For this reason, it takes a trained doctor relying on a library of knowledge and on your unique state in order to determine the ideal dosage. The "ideal dosage" is whatever provides the greatest benefit relative to the risk, keeping in mind that not treating or under-treating a disease carries its own risks.

3. The person's unique sensitivity to the substance and their health situation
Everybody is different, and therefore responds differently to a certain dose of a certain substance. Eating moderate amounts of wheat may be perfectly healthy and harmless to most people, but to a person with Celiac's disease, even eating a single wheat cracker can cause damage and discomfort. Similarly, a person taking a typical medicinal dose of morphine for the first time will not have a tolerance to the drug and therefore will respond much more strongly than a chronic morphine user taking the same dose. As another example, a person with high blood pressure is more at risk when eating large amounts of salt than the typical person. Whatever the substance may be, the safety of a certain dose depends on the individual's sensitivity. Furthermore, certain drugs can alter how strongly you respond to other drugs. Therefore, the safety of a certain medication depends also on what other medications you are taking. The bottom line is that whether a certain dose of a specific substance is the safest option depends on your unique health situation. Doctors document your height, weight, allergies, sensitivities, current medications, known diseases, and lab test results in order to prescribe the right dose of the right drug for your individual needs.

Since the safety of a substance depends on its toxicity, the dose, and on your unique health situation, the safest approach is generally to take the medications and the dosages prescribed by a competent medical doctor who is familiar with your health. Taking more medication than prescribed can be dangerous since the drug can build up to toxic levels that your body cannot handle. Taking less medication than prescribed can also be dangerous as it can allow your disease to continue causing harm. If you do not trust your doctor, then go see another doctor and get a second opinion. But simply avoiding medications because you are worried that they are not perfectly safe can lead to serious health problems later on.

If you look at the documentation that comes with any prescribed medication, you will see a long list of possible side effects. Such long lists of side effects can be alarming. This list does not mean that you will personally experience all or any of those side effects. Furthermore, this list does not mean that avoiding the medication is your safest option. If you were to avoid every medication and substance that has a long list of alarming side effects, you would be forced to avoid everything, including water. As shown below, even water has a long list of potentially serious side effects. But since water never comes from the store with all these side effects listed on the side, we often deceive ourselves into thinking that prescription drugs are dangerous in a way that water and food are not. The bottom line is that you should base your decision on whether to take a medication on the advice of your doctor, and not on the existence of a long list of side effects for the medication.

list of side effects of water
Even water comes with a long list of potential side effects. You should never base a medical decision only on the existence of a list of side effects. Public Domain Image, source: Christopher S. Baird.

Topics: allergy, body, dose, medication, medicine, pills, side effects, toxic, toxicity, water, water intoxication