How Serious Are The Side Effects Of Dietary Supplements?

There are negative effects of dietary supplements. But overall, the side effects of nutritional supplements tend to be minimal, both in frequency and severity. This is especially the case with vitamin side effects.

One of the biggest problems with dietary supplements and risks are not the actual, active ingredients themselves. No, the real issue are toxic contaminants, which are quite frequently contained in nutritional supplements, representing one of the more serious risks of taking dietary supplements.

Why supplement adulteration?

It is because the quality of most health supplements in the United States is only low-to-mediocre, due to a weak regulatory framework (as discussed in the 3-part article on "Exploring The Shady World Of Dietary Supplement Regulation". PART 1: Dietary Supplement Regulation -Is Supplement Quality Assured?).

Those natural health products that cause the most side effects of dietary supplements are oftentimes contaminated, manufactured incorrectly, or are taken either irresponsibly or improperly.

Nevertheless, one of the facts about dietary supplements is that, overall, the health risks with dietary supplements are low.

The good news?

Contaminated products, conceivably one of the greatest supplement risks (especially over time), can be easily avoided by taking high-quality, science-based, pure vitamins and supplements.

What Exactly Is A Side Effect?

A side effect, whether negative (harmful) or positive (beneficial), is any outcome or reaction be”side”, or next to, the main effect of a substance or nutrient.

In general, however, side effects of dietary supplements imply a damaging or toxic reaction, rather than a beneficial event. Consequently, other frequent interchangeable terms for side effects are adverse effects, adverse events, negative side effects, or toxic side effects.

In brief, side effects generally describe an adverse, toxic reaction alongside the primary beneficial, therapeutic effect of a particular substance.

An adverse event, or side effect, is the result of some form of unfavorable interaction of a substance with the chemical composition, or molecular structure, of the human organism. In many cases, a negative side effect entails the interference, blockage, or suppression of a physiological process within the human body. Or, the actual destruction of essential vital nutrients, cells, tissues, or even organs.

All Substances Have Side Effects

“The first rule of toxicology is that all chemicals [=both synthetic and natural] are "toxic chemicals;" it is the dose that makes the poison.” (Ames, et al., 1990, Pgs. 7782-6) [explanation added]

Yes, you can take too much vitamins. Yes, you can take too much minerals. Yes, you can take too much antioxidants...

Virtually any substance or particle on the planet, natural or man-made, can cause side effects if taken at a large enough dose or over a long enough time period.

Even water or oxygen are not exempt.

It is mostly a matter of dose/time-dependency, and the body's biological requirement for it. (Although, there are notable exceptions to the basic principle of dose-time dependency –such as with ionizing radiation, for example [covered in my book on The Honest Truth About Mammograms]).

On the official U.S. FDA website it states:

“When consumed in high enough amounts, for a long enough time, or in combination with certain other substances, all chemicals can be toxic, including nutrients, plant components, and other biologically active ingredients. (Official US Government FDA website, accessed Oct. 2011) [emphasis added]

The general toxicity principle of dose-dependency goes way back to Paracelsus (1493-1541), an educated but unconventional doctor, who is accredited with being the first person suggesting the connection.

Therefore, it is not unusual that something can elicit side effects. Naturally this includes encountering adverse effects of dietary supplements.

And the toxicity of a compound or particle does not necessarily depend on whether it comes from nature or is man-made. Eating a very poisonous mushroom is probably going to kill you even if you gathered it out in the woods.

Most Common Side Effects Of Dietary Supplements

Because in life anything and everything has risks, certain health risks of dietary supplements do exist.

Therefore, there are vitamin supplement side effects. There are niacin side effects. There are herbal side effects. There are omega 3 side effects. There are side effects of turmeric. There are side effects from nutritional diet supplements. And so forth, across the entire spectrum of food supplements.

However, because vitamins and supplements, as a whole, are extraordinarily safe the majority of adverse effects of dietary supplements are benign in nature.

Some of the most common adverse reactions (Hausman, 1989) are:

• Nausea
• Lethargy
• Diarrhea
• Constipation
• Headaches
• Skin rashes
• Vomiting
• Weakness
• Irritability

Best of all, practically all harmful effects of dietary supplements are reversible (Hausman, 1989). Usually within days or a few weeks upon discontinuation of the offending ingredients or products.

The Fundamental Question About Side Effects Of Dietary Supplements...

In regards to negative effects of nutritional supplements (or supplement ingredients), and actually about any substance whatsoever, the most critical question centers around what the probability or likelihood is of experiencing toxic or serious side effects.

In other words, what are the odds or the risk that something is going to harm you in significant ways?

To reiterate, toxicity (and efficacy) of a substance is commonly dose/time-dependent. Generally, the smaller the amount of a substance and the shorter the time frame leading to a side effect, the more toxic the substance. Conversely, the higher an amount of an element is needed and the longer the time interval to bring forth a side effect, the less toxic the compound is.

This also means that, in general...

The more toxic a substance is... the higher the risk for harm, the less safe, the less beneficial it is. Delivering fewer (if any) health gains.

On the other hand, the less toxic a substance is... the lower the risk for harm, the safer, the more beneficial it tends to be. Providing huge health gains.

Let's look at an example...

For very toxic substances, such as mercury, arsenic, or radioactive plutonium, for instance, the consumption of a tiny dose of any of these agents causes severe harm and destruction. These “potions” are extremely unsafe, they deliver virtually zero health benefits.

Conversely, to illustrate the situation with negative side effects of dietary supplements...

Vitamin C –a sugar-like material (a glucose analogue) that, therefore, had originally been called “ignose” (by its discoverer, Nobel Prize Laureate Albert Szent-Györgyi, PhD, MD, 1893-1986) and later “hexuronic acid” and then, finally, “ascorbic acid” or simply “vitamin C” (Stevens, 2017)– is extremely non-toxic. It is one of the least toxic of all substances known to science (Pauling, 1970). It requires huge doses to bring about side effects. And if vitamin side effects do occur from L-ascorbic acid, they probably will be minor. The potential of overdosing is small. This makes vitamin C exceptionally safe. And the benefits of vitamin C are outstanding.

Why Are Supplement Ingredients Exceptionally Safe?

The answer to that question is that the actual active supplement ingredients, most often, are substances or nourishing elements commonly found in food.

So, to make a very broad generalization...taking supplements is basically like eating food, or parts of food.

Food consists of the nutritional parts and compounds essential for human health and life. Fats, carbohydrates, proteins, water, vitamins, and minerals are among the key elements. Those are the basic nutrients your body must have to thrive. Your body is made out of these essential nutrients (and hopefully nothing else such as toxins).

Nutritional elements contained in wholesome food are what the cells of your body must have for optimal health and vitality.

Therefore, the truth about nutritional supplements and side effects is that...

Supplement ingredients, inherently, are exceptionally safe. Respectively, they have a relatively low innate potential for toxicity.

This high degree of supplement safety, this low risk of toxicity, is the reason why...

In general, there are relatively few side effects of dietary supplements, especially serious in nature.

The US government, quintessentially, corroborated this optimistic view about the scope of adverse effects of dietary supplements:

“[...] millions of Americans responsibly consume multi-vitamins and experience no ill effects.” (Official US Government FDA website, accessed May 2009)

Moreover, essential nutrients, which are commonly contained in nutritional supplements, are not just very safe for the human body... they are also commonly very beneficial.

Vitamin benefits are almost legendary. The health benefits of vitamins and the benefits of supplements in general are well-documented and verified by thousands of scientific studies and substantial clinical experience.


As I had mentioned above, all substances have side effects. It is inaccurate to assume that just because a nutrient is essential it is unconditionally safe or beneficial. Any element, essential or not, is toxic (unsafe) to one degree or another. For example, L-tryptophan, conceivably the most toxic amino acid, neatly exemplifies this caveat (addressed in the article Tryptophan Side Effects: L-Tryptophan Is Far From Harmless).

Which Supplements Have The Most Side Effects?

-Harmful Dietary Supplements

As a rule, adverse effects of dietary supplements depend on the toxicity potential of an ingested substance or food product.

Nutritional supplements commonly consists of both active and inactive ingredients.

That means that side effects of supplements are either caused by the actual active ingredients, or some inactive extraneous substances, such as contaminants, contained in the actual product (or their combined interaction).

Naturally, the improper use of substances or products will inevitably raise the risks for dietary supplement side effects since toxicity is dependent on dose (and time), independent from its source.

Contaminated Supplements

The worst offenders of supplement contamination cases are found among weight loss and sexual enhancement products, and sports enhancement and body building supplements (News & Events -Press Announcements, Dec. 15, 2010, from Official US Government FDA website, accessed Feb. 2011; Cohen, et al., 2014; Tucker, et al., 2018).

These categories of nutritional supplements cater to markets with huge demands. For instance, the majority of the US population is overweight. Millions of people are desperately trying to lose weight. The situation presents a heavenly haven for supplement promoters and suppliers to make quick and substantial profits -especially with some fad nutritional weight loss supplement.

It is not uncommon, therefore, to find low-quality discount vitamins and nutritional supplements among weight loss, sexual enhancement, and bodybuilding products. Some of them, unfortunately, are spoiled and tainted with impurities and various contaminants (Hendset, et al., 2005; Buettner, et al., 2009; Tucker, et al., 2018), which makes them potentially harmful dietary supplements.

These categories of products, more often than not, contain stimulants to achieve their advertised promises. Stimulants are introduced into the supplements by way of contaminants, such as prescription drugs, amphetamine-like compounds, or steroids for example (News & Events -Press Announcements, Dec. 15, 2010, from Official US Government FDA website, accessed Feb. 2011).

And stimulants come from an additional source, herbs.

Herbs... Mostly “Guilty By Association”

Stimulants of herbal or botanical origin are also routinely and prominently found in those three categories of nutritional supplements.

Abuse of herbal stimulants is common, in a number of ways.

For example, the herbal stimulants are often incorporated inappropriately into a product formulation. Numerous herbs with constituents that exert a stimulating effect have been used in the form of whole herbs for thousands of years without major safety issues.

However, some nutritional supplement manufacturers extract and concentrate the stimulating active herbal elements, and then either pack them into a single, stand-alone, artificially-spiked product or include them, along other nutrients, in the ingredient formulation of certain supplements. Oftentimes in weight loss supplements, sexual enhancement, and body building products.

Of course, side effects of dietary supplements are more likely to occur with these altered, enhanced products due to their artificially manipulated composition profile which, for example, raises the health risks of diet pills.

Furthermore, the improper use of these riskier types of herbal dietary supplements or botanical extracts contained in these three categories of products, implicates them in more cases of adverse effects of dietary supplements. This is especially a danger because the massive public demand for the purposes these particular nutritional supplements are used for, encourages irresponsible or indiscriminate usage.

Beyond that, herbs and botanicals are frequently contaminated.

In a scientific paper, released by the US government, the authors stated:

“Most of the documented examples of acute toxicity caused by botanical dietary supplements have been caused by the substitution of toxic plants for the desired species, probably through misidentification or production errors, or by contamination with pharmaceutical agents, either as a result of poor manufacturing practices or adulteration.” (van Breemen, et al., 2008)

In a report on the history of adulteration of herbs and spices, the author noted about the present state of affairs thereof:

“[...] the unfortunate situation appears to be that there may be numerous cases of accidental and intentional adulteration of herbal ingredients […].” (Foster, 2011)

Although herbs and botanicals oftentimes do contain essential nutrients for human life -such as vitamins, minerals, and amino acids- they do consists of many other non-essential constituents, frequently in dominant ways.

Because of the presence of numerous plant components which are “foreign” to the human physiology, herbs, in general, tend to be less safe than vitamins and minerals for instance. That is, the risk of harmful effects of dietary supplements with herbs and botanicals is higher. Plant-based food items contain many natural substances that are potentially toxic to humans (Ames, et al., 1990, Pgs. 7777-81). (Although, numerous non-essential herbal constituents also have shown to be very beneficial, especially in fighting health issues.)

This makes some supplement ingredients, such as herbs and botanicals, inherently more toxic:

“Although most botanical dietary supplements have health benefits and can be considered safe, [...], a few contain compounds, which can be converted to reactive intermediates causing toxicity.” (Dietz & Bolton, 2007)

The official data corroborates that herbs and botanicals tend to generate the most adverse effects of dietary supplements (American Association of Poison Control Centers, 1983-2008; GAO, 2009).

Toxicology reports suggest that the worst herbal side effects are most often the result of liver injury, which, however, is fairly uncommon (Willett, et al., 2004). Some very rare cases of liver failure involved the herbs ma huang and kava kava (Willett, et al., 2004).

These toxicological findings makes sense, since any non-body-innate or orthomolecular substance is ultimately a poison to the organism, to one degree or another, and will get subjected to detoxification processes. The main organs of detoxification are the liver and the kidneys. This relationship is also the reason why many drugs, and OTC medications such as ibuproven, cause damage to the liver and kidneys, including hepatitis, liver and kidney failure.

Of course, among the many different herbs and botanicals, varying degrees of toxicity exist.

According to a US government report the herbs kava kava (also referred to as just "kava") and lobelia have a high risk of causing dietary supplement side effects, including -at large doses- coma and death, which prompted a number of countries (but not the USA) to ban their sale (GAO, 2009). Yohimbe has caused some deaths, ginseng too has been implicated with deaths (American Association of Poison Control Centers, 1983-2008), and ma huang (ephedra) has been banned by the FDA in 2004 after a few people had died.

In many or even most of these case, however, the herbs had not been used as indicated, or as traditionally recommended. Ma huang, for example, has been used safely for thousands of years in Chinese medicine, primarily for respiratory afflictions such as asthma, or congestive issues due to the common cold. In the cases of death involving the herb it was inappropriately used for weight loss and as a stimulant to improve athletic performance, frequently as a highly concentrated extract rather than in the form and at the safety platform of a whole herb, as traditional application suggests. (Weight loss pills frequently contain concentrated botanical extracts that may pose a serious danger - see Do Garcinia Cambogia Side Effects Boost Diabetes?).

The FDA never provided any scientific proof that the herb, as used traditionally, is a health risk. FDA's removal of ma huang/ephedrine involved more politics than reasonable judgment.

Consider this...

Two of the main active ingredients in ma huang (ephedra) are ephedrine and pseudoephedrine, both of which are commonly found in over-the-counter medicines for respiratory ailments such as asthma and congestion. Over-the-counter cold preparations containing these two substances have either caused, or have been implicated with, numerous deaths (American Association of Poison Control Centers, 1983-2008).

Yet, those products are not banned.

The fact is...

Compared to many other “non-body-innate”, non-orthomolecular compounds, such as substances found in over-the-counter drugs and prescription medications, herbal dietary supplements and botanicals are multiple times safer, generally, just study the data of the American Poison Control Centers to validate this for yourself (American Association of Poison Control Centers, 1983-2008).

Herbal medicine has a very long tradition-of-use. It is conceivable that, over time, humans have slowly developed an acquired tolerance or better coping mechanisms to some or many of the potentially injurious substances contained in these botanical species of nature. Especially since much of humankind has been using and consuming a wide variety of herbs and spices for aeons.

Some compelling evidence supports this notion.

For instance, compared to synthetic chemical pollutants (toxins) the human body appears to be significantly more capable and efficient in detoxifying plant toxins, such as phytoestrogens (Zava, et al., 1997).

So what's the reality about the toxic effects of dietary supplements involving herbs and botanicals?

In most cases of side effects the actual herbs and botanicals are simply “guilty by association”. Because the final supplement products are either tainted with contaminants, due to poor supplement quality, or because these natural health products are used improperly.

Incidentally, the situation of herbal side effects describes precisely the general situation about the overwhelming majority of side effects of dietary supplements...

Safe Ingredients Versus Contaminated Products

It is not uncommon for people who bash food supplements to ignore the crucial difference between extremely safe active ingredients and tainted products (due to low manufacturing quality standards), and to omit disclosing the dissimilarity to the unsuspecting public. Usually because of ulterior motives, or out of pure ignorance.

The government itself has played tricks with this, primarily because of supplement politics, and has taken advantage of the widespread public ignorance about this important difference. The infamous incident of 1989 (see L-Tryptophan: The Truth About The FDA Tryptophan Recall Of 1989), implicating certain tryptophan supplements and the ensuing regulatory repercussions, is a rather fitting example of this type of deceptive maneuver (albeit tryptophan has its inherent problems).

The the truth about nutritional supplements and side effects is that the actual active ingredients are almost never the real problem.

They are simply “guilty by association”.

This means that the relatively few cases where people experience negative effects of dietary supplements are almost always tied to products compromised in quality, or improper product use.

In a sense this is promising...

Because by choosing, and using properly, high-quality, science-based, pure vitamins and health supplements you virtually eliminate all side effects of dietary supplements.

(Originally published: ca. July-2012 | This is an updated version)

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Article Index On Side Effects Of
Dietary Supplements And Risks



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