Can Dietary Supplements & Vitamins Cause Dangerous Side Effects?

Here’s a quick fact: None of the vitamins or dietary supplements glaring at you from store shelves have been reviewed for safety or effectiveness by the FDA, or any other organization for that matter, before you to buy them.

Instead, the ingredients they contain are only required to be classified as “generally safe,” while their labels can’t be “misleading.” Proof of benefit and disclosure of risk from the manufacturer is not required in any way.

Emphasizing just how alarming this could be, in her book Vitamania, Catherine Price writes: “The scariest supplements are not the ones that are totally ineffective; they’re the ones that actually do stuff, since—thanks to DSHEA—manufacturers are not required to study exactly what they’re affecting, how they work, or what their long-term effects may be (let alone how they interact with other ingredients, foods, or drugs).”

Can dietary supplements & vitamins cause dangerous side effects? To help you answer this question, we enlisted the help of industry professionals. Ready to begin?

How Common Are Vitamin & Dietary Supplement Side Effects?

According to an article published in the New England Journal of Medicine titled Emergency Department Visits for Adverse Events Related to Dietary Supplements, between 2004 and 2013, about 2,150 people were hospitalized each year in the U.S. due to side effects caused by vitamins or dietary supplements.

However, this data might not provide a complete picture of the situation, since the American Cancer Society reports that in 2013 alone, more than 100,000 calls were made to U.S. poison control centers related to exposure to supplements—only 8,000 of which were treated in healthcare facilities.

They also emphasize that, “Most people who suffer unexpected side effects, illnesses, or drug interactions from dietary supplements don’t call a poison control center or the supplement manufacturer. This means that the numbers we have are likely very low estimates of actual events.”

Which Supplement Side Effects Are Most Commonly Reported?

Based on the data in this article, weight loss and energy products accounted for more than half of the visits for those between 5 and 34 years old, while patients 65 or older most often reported adverse effects related to iron, calcium, and potassium supplementation. Like what, specifically?

The most commonly reported side effects were related to cardiac symptoms (palpitations, chest pain, or rapid heart beat), along with allergic reactions and swallowing problems.

Given this information, when answering the question, “Can vitamins and dietary supplements cause dangerous side effects?” we can see there are a variety of factors that can impact the answer. After all, as we discuss in The History of Dietary Supplements, vitamins and supplements aren’t just one ‘thing.’

The bottom line is that the side effects someone might experience could vary, depending on:

  • The specific ingredient
  • How much of the ingredient they ingested
  • Whether or not the supplement contained any ingredients not listed on the label, including prescriptions drugs or other unintended contaminants
  • The person’s age
  • Other prescription medications or supplements the person might be taking
  • Current medical conditions

We’ll wrangle this massive topic into easily digestible bites below by breaking everything down into two categories: potential overdose situations and drug interactions.

What Are the Most Common Side Effects From Taking Too Many Vitamins?

We’ve frequently discussed the importance of the 13 essential vitamins in the past, as well as the fact that hundreds of additional minerals and substances exist—like omega 3 (fish oil), fiber, selenium, resveratrol, and so forth—that have clinical support indicating they may provide some health benefits.

And according to Vasilios Frankos, Ph.D., Director of FDA's Division of Dietary Supplement Programs, the good news is that “Vitamins are not dangerous unless you get too much of them.”

Arielle Levitan, MD, and co-founder of Vous Vitamins, takes this thought one step further by recommending, "As a physician and vitamin expert, I would say it is very important for people to realize that taking too much of or the wrong vitamins and supplements can be very dangerous. We have seen patients end up on the liver transplant list from high doses of niacin. We have seen patients end up in the ICU near comatose from a vitamin D overdose.”

To this extent, most of the U.S. population already receives adequate vitamin levels from fortified foods, and therefore may not be deficient. Thus, taking some vitamin supplements could cause you to exceed the safe upper limit (SUL) leading to some potentially dangerous side effects like: 

Ingredient Safe Upper Limit Potential Side Effects Caused by Excessive Dosing
Vitamin A 10,000 IU Nausea, headache, fatigue, dizziness, dry skin, and even psychiatric changes and osteoporosis with long-term overuse.
Vitamin B6 100 mg Extended high-dose supplementation can lead to permanent nerve damage and loss of bodily movement control.
Vitamin C 2,000 mg Can increase the risk of kidney stones.
Vitamin D 600 – 800 IU In some instances, high vitamin D supplementation is required under medical supervision. However, if taken long-term, it can lead to excessive calcium levels in the blood.
Vitamin E 1,100 – 1,500 IU Could increase the risk of stroke, as well as a slight increase in the likelihood of death from all causes.
Calcium 2,000 – 2,500 mg Too much over a long period of time may increase the risk of heart attack.
Echinacea Unknown (300 mg dry powdered extract or 0.25 to 1.25 mL liquid extract 3X daily have been used) Rare – mostly related to temporary digestive upset.
Fish Oil 3 g May reduce immune system function and decrease blood clotting ability.
Folic Acid 1,000 mcg May increase risk of heart attack, along with the risk of lung or prostate cancer, irritability, and behavior changes.
Ginkgo Unknown (it’s recommended that you start at 120 mg per day) May increase risk of bleeding and bruising, decrease the ability to form blood clots.
Green Tea Unknown Due to the natural caffeine content, excessive doses can cause insomnia, jitteriness and nervousness, and irregular heartbeat. This could be more pronounced in those who are sensitive to stimulants.
Iron 45 mg Excessive doses/poisoning can lead to liver failure, low blood pressure, and even death.
St. John’s Wort 900 mg Can increase severe reactions and sensitivity to sun exposure.

As we can see, even some of the most essential nutrients can be dangerous—or deadly—if regularly consumed in too-high doses, which is why it’s always important to speak with your doctor about any vitamins (along with the doses) you’re taking.

Now, let’s move on to potential interactions with prescription medications.

What Are the Most Common Drug Interactions Caused By Supplements & Vitamins?

Even when not taken in excessive doses, supplementation of some of the most popular (although not necessarily essential) vitamins and other minerals can cause potentially dangerous interactions with pharmaceutical drugs. Like what?

Karen Morse, a public health professional and Drug Safety consultant who has been working in the industry for 17 years, kicks things off:

“One of the first things that come to mind is St. John's Wort, a natural remedy for supporting mood disorders. There are over 800 documented drug interactions between it and prescription/OTC drugs, which range from lack of drug effect (St. John's Wort plus oral contraceptive can render the birth control ineffective resulting in pregnancy) to interaction with many cardiac and pain medications.”

Sydney Ziverts, Health and Nutrition Investigator for, mirrored this concern about St. Johns Wort, but also added that, “if calcium is combined with antibiotics, it can reduce the effectiveness of the medication, and if it’s combined with antihypersensitives (high blood pressure medication), severe kidney damage can occur. Melatonin can also increase or decrease the efficacy of diabetes medications.”

Suzanne Robotti, health advocate and president/founder of MedShadow Foundation, an online nonprofit that informs the public about the side effects, risks, and benefits of over the counter medication (including supplements) and prescription drugs, adds that “omega-3 supplements can adversely interact with blood thinning medications or NSAIDs because of their anti-clotting properties.”

“Concentrated herbal supplements can contain substances that cause miscarriage, premature birth, uterine contractions, and more. Further, supplements can interact with other medications consumers may be taking,” Suzanne also told us.

According to WebMD and Natural Database’s summarization of the available clinical evidence, other possible interactions for common vitamins and dietary supplements include: 

Ingredient Potential Drug Interactions
Vitamin A May interact with diabetes medications, those that lower cholesterol, and gout drugs.
Vitamin B3 Moderate potential reactions with alcohol, medications for gout and diabetes, and those that lower cholesterol and blood pressure.
Vitamin B6 In some instances, can decrease the effectiveness of Phenobarbital and phenytoin.
Vitamin B12 A potential major interaction with chloramphenicol, which is used to produce new blood cells.
Vitamin C Can reduce the effectiveness of blood thinners, cancer drugs, and HIV/AIDS medications, while increasing side effects caused by estrogen therapy.
Vitamin D Can reduce the effectiveness of antihypertensives and cholesterol-lowering statins.
Vitamin E May reduce the effectiveness of cancer drugs, increase the risk of side effects from immunosuppressive drugs, and increase the effect of blood thinners.
Vitamin K A major potential interaction with blood thinning medication, since this vitamin helps blood clot.
Calcium Calcium supplementation may cause a major interaction with ceftriaxone (life-threatening damage to the lungs and kidneys), as well as moderate interactions with some antibiotics, diltiazem, levothyroxine, and verapamil.
CoQ10 Can reduce the effectiveness of blood thinners and cancer drugs, while increasing the effect of antihypertensives.
Echinacea May interact with caffeine and medications that are changed by the liver, or that decrease immune system response.
Fish Oil/Omega 3 May reduce the effectiveness of cancer drugs and increase the effects of antihypertensives and blood thinners.
Folic Acid Can decrease the effectiveness of Fosphenytoin, methotrexate, Phenobarbital, phenytoin, primidone, and pyrimethamine.
Ginkgo Major potential interactions with ibuprofen, medications that slow blood clotting, and warfarin. Moderate interactions include alprazolam, buspirone, fluoxetine, and those changed by the liver.
Panax Ginseng Moderate interactions with caffeine, furosemide, insulin, depression medications, diabetes medications, and stimulant drugs like epinephrine and pseudoephedrine.
Glucosamine A major potential interaction with medication for slowing blood clotting and a minor interaction with some cancer medications.
Green Tea The natural caffeine content may cause major interactions with amphetamines and other stimulants. Moderate interactions include some antibiotics, birth control pills, clozapine, estrogens, lithium, and depression medications.

Given all these potential side effects, some of which could be very dangerous, how can consumers stay safe?

How Can You Avoid Potentially Dangerous Side Effects From Dietary Supplements & Vitamins?

On their What You Need to Know About Dietary Supplements page, the Food and Drug Administration clearly states:

“The manufacturers and distributors of dietary supplements are responsible for making sure their products are safe BEFORE they go to market.

If the dietary supplement contains a NEW ingredient, manufacturers must notify FDA about that ingredient prior to marketing. However, the notification will only be reviewed by FDA (not approved) and only for safety, not effectiveness.”

Based on this, along with our research and interviews with professionals, a clearly recurring theme is apparent:

If you’re thinking about taking a vitamin or supplement, the first thing you should do is speak with your healthcare provider. They can help you gain a clearer understanding of whether or not it would be safe and beneficial, based on your specific diagnosis.

Karen Morse seconds this recommendation: “One of the smartest things you can do as a consumer is to share any and all vitamins and supplements you are using with your physician and your pharmacy (also, using one pharmacy to fill all Rx meds is recommended). Many pharmacies will enter all of your current medications (including supplements) into your file, and when a doctor calls in a new order for a prescription, a flag will be raised in the database regarding a potential interaction, an allergy, or other caution that is specific to each patient. This could be potentially life-saving in some situations.”

In addition, the FDA recommends using non-commercial sites like the National Institutes of Health and USDA to research supplements and their ingredients, since these organizations have no financial interest in your decision. This certainly includes consumer feedback on review sites like HighYa.

They also note that you should be mindful of product claims such as:

  • “Works better than [a prescription drug]”
  • “Totally safe”
  • “No side effects”
  • And be aware that the term ‘natural’ doesn't always mean ‘safe’

Arielle Levitan, adds that “One way to help ensure a quality product is to look for USP or GMP certification, which suggests that there is some degree of self-regulation on the part of the company. Be especially careful with herbal products. Also, anything that makes big claims about energy, weight loss, or the like is highly suspicious and could possibly contain illicit hormones or stimulants.”

And if, along with your doctor’s help, you’ve narrowed your options down to a few choices, don’t be shy about contacting the manufacturer or distributor directly regarding information to support their claims, along with details about the supplement’s safety and effectiveness. In our experience, their responses to your questions can speak volumes about their business ethics.

See Also: Homeopathy: Evidence-Based Medical System or 200-Year Old Scam?

Derek Lakin

With more than a decade of experience as a copywriter, Derek takes a detail-oriented, step-by-step approach to help you shop smarter. Whether it’s nutritional supplements or new scams, he believes an informed consumer is a happy customer.