The potential side effects of dietary supplements

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Much like prescription medicines, dietary supplements come with the potential for unwanted side effects. There are currently no requirements for clinical studies to verify the safety or even potency of a dietary supplement, as they are technically not allowed to claim any health benefits. Supplements also do not require a doctor’s prescription, making the vast majority of supplement use self-prescribed. This often means that people begin taking supplements without informed medical guidance.

Many supplements contain active ingredients that can have varied and serious effects within the body, some desired, some not. In some cases, taking too much of a supplement can have serious complications. For example, some supplements can have unwanted effects before, during, and after surgery.[1] Supplements can also interact with prescription medicines to reduce or increase their activity, or to produce other unwanted side effects. Between 2008 and 2010, the American Association of Poison Control Centers (AAPCC) received 145,775 calls related to the side effects of dietary supplements, and the FDA (from 2008 to 2011) received 6,307 similar reports.[2] However even these numbers are still likely to dramatically underestimate the true scope of the situation, as most people suffering from unexpected side effects, illnesses, or drug interactions do not call a poison control centre or report the adverse reaction to the manufacturer of the supplement. 

Potential supplement side effects can include gastrointestinal symptoms,[3]  liver toxicity,[4] heart attacks,[3] and even cancer.[5] Although these side effects can be serious and even fatal, consumers in general do not appreciate the risks. The use of the term “natural” on the product label often fools many into believing that the product is safe and can do them no harm, and the important ‘small print’ is often ignored. In addition to this, supplement manufacturers are not legally bound to indicate potential side effects on the product label. Increasingly popular diet and ‘muscle-building’ supplements can be some of the most dangerous. These types of supplements often contain stimulants which suppress the appetite, but which can also raise the blood pressure to dangerously high levels and increase the risk of a heart attack or stroke.[6]

Whilst supplements can be beneficial to many users, individuals can react differently. Side effects can be experienced when using too high a dose of a product, when taking the recommended dose, or even when taking a less than recommended dose. Some supplements are marketed as having “almost no side effects”, but when combined with other substances, or taken too frequently, can quickly become toxic.[7] Vitamin C, for example, is often taken frequently to ‘boost’ the immune system, but taken in large amounts can cause diarrhoea. Other, more serious side effects are also possible - for example, the risk of lung and stomach cancers is significantly increased in those who consume 20-30mg/day of B-carotene.[8] In those taking calcium supplements, one study demonstrated a doubling of hospital admissions for gastrointestinal problems, a 17% increase in kidney stones and a 20-40% increase in the risk of a heart attack.[9]

Once a side effect is found to be the result of dietary supplement intake in an individual, simply stopping taking the supplement will often lead to resolution of the side effect.[10] However this is not always the case, and some supplements can have longer-lasting effects, especially those with the potential for serious and even fatal side effects, such as cancer or increased risk of a heart attack. 
Given this potential for serious and even fatal side effects, sound advice would be to think twice before opting to take dietary supplements and at the very least consulting your doctor before taking them, particularly if you are taking prescription medication. If, when taking supplements, you begin to develop side effects or symptoms, you should stop taking the supplement and consult your doctor before it is too late.


[1] Wang, CZ, Moss, J, Yuan, CS. (2015) Commonly Used Dietary Supplements on Coagulation Function during Surgery. Medicines (Basel). 2(3). 157-85.

[2] GAO (2013) Dietary supplements FDA may have opportunities to expand its use of reported health problems to oversee products. Retrieved April 2016 from, 

[3] Reid, IR, Bristow, SM, Bolland, MJ. (2015) Calcium supplements: benefits and risks. J Intern Med. 278(4). 354-68.

[4] Haslan, H, Suhaimi, FH, Das, S. (2015) Herbal supplements and hepatotoxicity: a short review. Nat Prod Commun. 10(10). 1779-84.

[5] Harvie, M. (2014) Nutritional supplements and cancer: potential benefits and proven harms. Am Soc Clin Oncol Educ Book. e478-86.

[6] CDC (1996) Adverse events associated with ephedrine-containing products--Texas, December 1993-September 1995. MMWR Morb Mortal Wkly Rep. 45(32). 689-93.

[7] Mulholland, CA, Benford, DJ. (2007) What is known about the safety of multivitamin-multimineral supplements for the generally healthy population? Theoretical basis for harm. Am J Clin Nutr. 85(1). 318S-22S.

[8] Druesne-Pecollo N, et al. (2010) Beta-carotene supplementation and cancer risk: a systematic review and metaanalysis of randomized controlled trials.Int J Cancer. 127(1). 172-84.

[9] Reid, IR, Bristow, SM, Bolland, MJ. (2015) Calcium supplements: benefits and risks. J Intern Med. 278(4). 354-68.

[10] Felix, TM, Karpa, KD, Lewis, PR. (2015) Adverse effects of common drugs: dietary supplements. FP Essent. 436:31-40.


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