The Ultimate Supplement Guide: What the Evidence Actually Says About What's in Your Medicine Cabinet
A Coworker, a Senior Center, and a 6.8-Trillion-Dollar Question
A few weeks ago, a coworker pulled me aside in the Emergency Department and asked me a version of a question I hear on almost every shift: "Dr Cois, are there any vitamins or supplements I can take to stop getting sick all the time?"
It's a completely reasonable question. It is also a question the wellness industry has built a six-point-eight-trillion-dollar global enterprise around answering — almost always with something to sell you. The honest clinical answer I gave her is one you rarely hear from an influencer with a discount code: the evidence that any supplement meaningfully prevents respiratory viral illness is weaker than the marketing suggests, and the biggest levers to avoid getting sick are not in a bottle. Hand hygiene. A well-fitted N95 when exposure is high. Staying current on your influenza and COVID vaccinations.
A few months earlier, I cared for an older gentleman living on Social Security — roughly sixty dollars a day. He presented with some nausea and diarrhoea, nothing requiring admission. What made the case memorable was the social history. He ate his lunches and dinners at the local senior centre because the meals were free. And in the same breath, he told me he was spending a portion of his fixed income on a herbal supplement someone had told him would improve his gut health.
A man who could not afford his own groceries was being separated from a portion of his income by a supplement company. That image, more than any meta-analysis, is what convinced me this topic deserved its own episode. The supplement industry is, in many cases, grifting off of the vulnerable — and the vulnerable are not always who you'd expect. They include your grandmother, the exhausted coworker, and the patient who just got a cancer diagnosis and is looking for hope in a bottle.
Why Supplements Are Regulated the Way They Are
In 1994, Congress passed the Dietary Supplement Health and Education Act, or DSHEA. Under DSHEA, a dietary supplement does not need to be proven safe before it reaches the shelf. It does not need to be proven effective. The FDA's authority is largely post-market — reactive, not preventative.¹ Contrast this with the approval pathway for prescription drugs and vaccines, which typically requires phase 1 through 3 randomised controlled trials, FDA review, advisory committee input, and post-market surveillance.²
That regulatory asymmetry is why supplement bottles use language like "supports healthy immune function" or "promotes joint comfort." Those are not clinical endpoints. They are marketing phrases engineered to stay on the permissible side of a regulatory framework that was designed around the needs of the industry being regulated.
The scale of that industry is worth pausing on. The global wellness economy is valued at approximately 6.8 trillion dollars per year, with projections to reach 9.8 trillion by 2029.³ The global pharmaceutical industry is valued at approximately 1.6 trillion dollars.⁴ The wellness industry is more than four times the size of the pharmaceutical industry. When a wellness influencer tells you your physician is "compromised by Big Pharma," it is worth asking which side of that transaction has more financial motive to move the product.
The Evidence Hierarchy: Five Supplements Worth Keeping (In the Right Context)
What follows is not a blanket endorsement. Each of these has a specific evidence base and a specific population in whom supplementation is reasonable.
Creatine monohydrate. This is the most well-evidenced supplement on the planet. A 2024 systematic review and meta-analysis in Nutrients by Wang and colleagues found that creatine combined with resistance training significantly increased muscle strength in adults under 50.⁵ A 2025 meta-analysis in the European Review of Aging and Physical Activity found statistically significant 1-rep max improvements in older adults adding creatine to exercise training across 20 studies and 1,093 participants.⁶ A 2024 meta-analysis in Frontiers in Nutrition demonstrated cognitive benefits — particularly for memory and processing speed — strongest in older adults and those in states of cognitive stress.⁷ The dose is 3 to 5 grams per day of creatine monohydrate. The caveat: creatine works with resistance training, not instead of it.
Vitamin D. A 2024 systematic review in the Journal of Clinical Endocrinology & Metabolism by Shah and colleagues — designed to support the Endocrine Society's updated clinical practice guidelines — screened 37,000 citations and included 151 studies.⁸ The honest finding: in healthy adults aged 19 to 74, routine empiric vitamin D did not significantly affect most clinical outcomes. In adults aged 75 and over, there was a small but clinically important reduction in mortality. In adults with prediabetes, there was moderate-certainty evidence of reduced progression to type 2 diabetes. In pregnancy, low-certainty evidence suggested maternal and neonatal benefit. A reasonable dose for most adults is 1,000–2,000 IU of vitamin D3 daily. High-dose intermittent regimens are associated with increased falls and should not be taken without physician supervision.
Omega-3 fatty acids. The VITAL trial, published in the New England Journal of Medicine by Manson and colleagues, randomised 25,871 U.S. adults to 1 gram per day of marine omega-3 or placebo for a median of 5.3 years.⁹ It did not significantly reduce the primary cardiovascular or cancer endpoints. High-dose prescription-grade icosapent ethyl in REDUCE-IT demonstrated a 25 percent reduction in major cardiovascular events in patients with elevated triglycerides on a statin — but that is a different product, at a different dose, in a different population than an over-the-counter fish oil softgel. For the general public, eating oily fish once or twice per week outperforms supplementation in the observational data.
Magnesium. The cheapest and most underrated supplement on this list. A 2024 umbrella meta-analysis by Alharran and colleagues pooled 10 review papers covering 8,610 participants and found magnesium supplementation produced statistically significant reductions in both systolic and diastolic blood pressure, most pronounced at doses ≥400 mg/day for ≥12 weeks.¹⁰ A 2018 systematic review by von Luckner and Riederer supports magnesium for migraine prophylaxis.¹¹ Typical dose is 200–400 mg of elemental magnesium per day; glycinate and citrate forms are well-tolerated.
Multivitamins. The COSMOS trial, published in the American Journal of Clinical Nutrition by Sesso and colleagues, randomised 21,442 older adults to a daily multivitamin or placebo.¹² The multivitamin group had a statistically significant 8 percent reduction in total cancer incidence. It is a modest signal, and it must be weighed against earlier trials — SELECT found vitamin E increased prostate cancer risk by 17 percent, CARET found beta-carotene increased lung cancer risk in smokers by 18 percent. More is not always better. For older adults with imperfect diets, a basic non-mega-dose multivitamin is reasonable nutritional insurance.
Four Supplements With Large Marketing Budgets and Small Evidence Bases
NAD⁺ precursors (NMN and NR). A 2024 systematic review by Zhang and colleagues in Critical Reviews in Food Science and Nutrition reviewed 4,049 records and included 12 RCTs with 513 participants.¹³ NMN did reliably elevate blood NAD levels. But the review found no significant effect on fasting glucose, triglycerides, cholesterol, or most other clinically relevant markers. The authors concluded that "an exaggeration of the benefits of NMN supplementation may exist in the field" — a remarkable sentence to find in a peer-reviewed meta-analysis. The FDA has declared NMN an investigational new drug, further clouding the regulatory picture.
Berberine. Marketed online as "nature's Ozempic." A 2025 meta-analysis in Frontiers in Pharmacology by Liu and colleagues included 12 placebo-controlled RCTs and found modest, statistically significant reductions in triglycerides, fasting glucose, LDL cholesterol, and waist circumference — in patients with metabolic syndrome.¹⁴ Not in healthy adults using it recreationally. The effect sizes are real but modest and are not comparable to GLP-1 receptor agonists. Berberine has meaningful drug interactions via CYP3A4 inhibition, and should not be used in pregnancy.
Collagen. A 2025 systematic review and meta-analysis by Myung and colleagues in the American Journal of Medicine analysed 23 RCTs with 1,474 participants and found collagen supplements improved skin outcomes overall — but when stratified by funding source, only industry-funded studies showed benefit.¹⁵ In non-industry-funded studies, there was no significant effect. High-quality studies showed no benefit; low-quality studies did. This is a textbook signature of publication and methodological bias. Dietary collagen is digested into constituent amino acids, which is exactly what any adequate protein intake already provides.
"Detox" and "cleanse" supplements. A 2015 review by Klein and Kiat in the Journal of Human Nutrition and Dietetics found no compelling evidence for commercial detox diets.¹⁶ The liver and kidneys are the body's detoxification system. The grift pattern to recognise: an online practitioner tests for vague markers ("inflammation," "food sensitivities," "gut dysbiosis") using unvalidated assays, finds abnormalities that were statistically guaranteed to appear, and then sells the protocol to fix them. When the same entity sells both the test and the fix, that is a sales funnel, not medicine.
A Word on Peptides and the February 2026 FDA Reclassification
In late 2023, the FDA placed 19 peptides on its Category 2 bulk drug substance list, restricting compounding pharmacies' ability to prepare them under Section 503A. On February 27, 2026, HHS Secretary Robert F. Kennedy Jr. announced that approximately 14 of those 19 peptides — including BPC-157, TB-500, CJC-1295, Ipamorelin, AOD-9604, GHK-Cu, Selank, Semax, and Thymosin Alpha-1 — would be moved back to Category 1.¹⁷ As of this writing, formal FDA rulemaking is still in progress, with advisory committee meetings scheduled through early 2027.
It is worth being precise about what that reclassification means. Category 1 status restores the legal pathway for compounding pharmacies to prepare a peptide under a physician's prescription. It does not mean the peptide has been FDA-approved. It does not mean phase 3 trials have demonstrated safety and efficacy. It means access through licensed pharmacies has been restored.
The strongest illustration of the evidence gap comes from BPC-157, the most-hyped peptide on social media. A 2025 systematic review in the HSS Journal by Vasireddi and colleagues screened 544 articles and included 36 studies — 35 preclinical animal studies, and one uncontrolled retrospective case series in 12 human patients.¹⁸ That is the entire peer-reviewed evidence base for a compound being sold across hundreds of clinics nationwide.
Contrast this with retatrutide — a triple-agonist peptide (GLP-1, GIP, glucagon) in phase 3 development by Eli Lilly. A 2024 meta-analysis of three RCTs involving 878 patients demonstrated mean weight reduction of over 14 percent versus placebo, with the phase 2 trial at 12 mg showing 24 percent mean weight loss at 48 weeks.¹⁹ Retatrutide is not yet FDA-approved precisely because it is being held to the standard of evidence we should expect — the same standard that brought us safe, effective GLP-1 medications for metabolic disease.
How Should This Modify Your Practice?
If you are a clinician reading this, I'd offer a few concrete suggestions for how to work through this with patients.
• Ask, without judgement, what your patients are taking. Many patients don't volunteer supplement use unless specifically asked, and some supplements have meaningful drug interactions — berberine with statins, St John's wort with serotonergic agents, high-dose vitamin E with anticoagulants.
• When a patient asks about a supplement, orient them to the Tier 1 versus Tier 2 distinction. Is their diet, movement, sleep, stress management, and primary care relationship locked in? If not, the supplement is a distraction from the signal.
• For older adults with imperfect diets, a basic multivitamin is reasonable (COSMOS evidence). For documented vitamin D deficiency, supplement accordingly. For hypertension, discuss magnesium as an inexpensive adjunct to diet and first-line pharmacotherapy. For those engaged in resistance training, creatine is well-evidenced and safe.
• For patients using peptides obtained outside a licensed physician-pharmacy relationship — grey-market BPC-157, TB-500, research-chemical vendors — counsel on the absence of quality control, the absence of human safety data, and the absence of dosing validation. Reclassification to Category 1 does not equal approval.
• Direct patients to Open Payments (openpaymentsdata.cms.gov) when conflict-of-interest questions arise. Transparency about physician conflicts is one of the strongest counterarguments to the "Big Pharma" framing — it exists for physicians, and has no equivalent for wellness influencers.
The One Thing to Do This Week
Take every supplement out of your cabinet or subscription list. For each one, ask three questions. Is there a specific medical reason I'm taking this — a documented deficiency, a guideline-based indication, a recommendation from my primary care physician? Can I name the evidence? And what is this costing me per month, and what could that money do somewhere else?
If the supplement does not pass those three questions, throw it out. Cancel the subscription. Redirect the money toward Tier 1 — a gym membership, a dietitian consult, a pair of running shoes, or your retirement account.
Fewer bad days. More good decades.
About the Author
Dr Adrian Cois is a board-certified Emergency Physician, former strength and conditioning coach, and the host of Overheard in the Emergency Room. He writes and teaches at the intersection of evidence-based medicine and everyday decision-making. Find more at drcois.com.
Disclosure: Dr Cois has no financial relationships with any supplement manufacturer, peptide compounding pharmacy, or wellness brand.
Related Reading on drcois.com
• Episode 11: Your Blood Testing Toolkit — What Your Doctor Actually Checks and Why
• Episode 8: Obesity — Stigma, Influencer Myths, and Guideline-Directed Care
• Episode 3: The Minimum Effective Dose of Exercise
• Episode 2: Food as First-Line Medicine — The 80/20 Plate
• Episode 1: The Tier 1 / Tier 2 Framework
References
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3. Global Wellness Institute. The Global Wellness Economy Hits a Record $6.8 Trillion and Is Forecast to Reach $9.8 Trillion by 2029. Accessed April 22, 2026. https://globalwellnessinstitute.org/press-room/press-releases/
4. IntuitionLabs. Global Pharmaceutical Market: 2025 Analysis & Key Trends. Accessed April 22, 2026. https://intuitionlabs.ai/articles/pharmaceutical-market-analysis-trends
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8. Shah VP, Nayfeh T, Alsawaf Y, et al. A Systematic Review Supporting the Endocrine Society Clinical Practice Guidelines on Vitamin D. J Clin Endocrinol Metab. 2024;109(8):1961-1974. doi:10.1210/clinem/dgae312
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14. Liu D, Zhang H, et al. Efficacy and safety of berberine on the components of metabolic syndrome: a systematic review and meta-analysis of randomized placebo-controlled trials. Front Pharmacol. 2025;16:1572197. doi:10.3389/fphar.2025.1572197
15. Myung SK, Park Y. Effects of Collagen Supplements on Skin Aging: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Am J Med. 2025. doi:10.1016/j.amjmed.2025.03.040
16. Klein AV, Kiat H. Detox diets for toxin elimination and weight management: a critical review of the evidence. J Hum Nutr Diet. 2015;28(6):675-686. doi:10.1111/jhn.12286
17. FDA to weigh easing limits on unproven peptides favored by RFK Jr. AP News. Published 2026. Accessed April 22, 2026. https://apnews.com/article/peptides-fda-kennedy-injection-bpc157-37bf2f94f0e8a57da76e67a03b58ff0f
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19. Abdrabou Abouelmagd A, Abdelrehim AM, Bashir MN, et al. Efficacy and safety of retatrutide, a novel GLP-1, GIP, and glucagon receptor agonist for obesity treatment: a systematic review and meta-analysis of randomized controlled trials. Proc Bayl Univ Med Cent. 2025;38(3):291-303. doi:10.1080/08998280.2025.2456441
