Compounds › Supplements and related compounds

Over-the-counter supplements

43 items with dose, from what has good evidence to what has only marketing

Partially approvedSupplements and related compounds

Experimental material. Read before using anything from here.

Nothing on this page is a medical recommendation, prescription or treatment plan. It is an organized translation of protocols circulating in research communities and, where it exists, of what published trials tested. The two are marked differently — and they are not equivalent.

Most of the compounds here have no FDA approval for human use. Several are sold labeled "research use only", which means they have not gone through purity, sterility or dosage controls for human consumption. A community-reported dose is not a validated dose: it is what someone reported having done.

Talk to a licensed health professional before considering any of these compounds. If you already use one and feel anything unexpected, seek care — do not wait for the next routine test.

Specific caution for this compound: Supplement doses also have a ceiling. Selenium, zinc, iodine, vitamin B6 and vitamin D have a defined tolerable upper limit — exceeding it brings no extra benefit, it brings risk. And melatonin, in Brazil, is only a supplement up to 0.21 mg per day.

Summary

Forty-three over-the-counter supplements with the dose range used in studies and on standardized labels, organized by purpose: vitamins and minerals, performance, sleep and cognition, longevity, gut and liver. Each carries the strength of the evidence and the caveat that matters — upper limit, drug interaction or a claim the data does not support. It is the only section of the site where most items have low risk and decent evidence, and that is why the dose appears.

How to read this page

Forty-three over-the-counter items, with the dose range used in studies and on the standardized label. Unlike the rest of the site, here most have low risk and real evidence — and that is why the dose appears.

The RCT/meta column gives the number of randomized trials and meta-analyses indexed in PubMed, checked item by item on September 4, 2026. All forty-three items on this page are checked: the thirteen that were left pending on the first pass were closed on the same date, with the same query.

Read the number carefully: a high count means many people studied it, not that the result was favorable. Ginkgo, on the herbal medicines page, is the caricature example of this.

Specific warning on two items

Melatonin: It is authorized as a dietary supplement only up to 0.21 mg per day for adults. The 0.5 mg and 3 mg presentations are above that limit and, in Brazil, do not qualify as an over-the-counter supplement.
Iron: only makes sense with deficiency proven by lab test. Supplementing iron without deficiency is accumulating a pro-oxidant metal with no gain at all, and it can mask the workup of a cause of anemia.

Vitamins and minerals

Feature	Usual range	For what	RCT/meta	Caveat
Vitamin D3	1,000–4,000 IU/day	Deficiency, bone health, immunity	3.625	4,000 IU/day is the IOM tolerable upper limit. The 5,000 IU presentation exceeds it — test 25-OH-vitamin D first
Vitamin D3 + K2	D3 as above + K2 (MK-7) 90–200 mcg	Directing calcium to bone	116	K2 interacts with warfarin. Anyone anticoagulated with a coumarin does not use it without guidance
Vitamin C	500–1,000 mg/day	Antioxidant, collagen, iron absorption	270	Above 2 g/day: osmotic diarrhea and risk of oxalate stones
Vitamin B12 (methylcobalamin)	500–1,000 mcg/day	Deficiency, above all in vegetarians and in people on metformin	436	Practically no toxicity. Testing first avoids supplementing what is not lacking
B complex	as labeled	Broad coverage of the B group	196	B6 above 100 mg/day over a long period causes peripheral neuropathy — it is the forgotten risk of the B complex
Magnesium glycinate	200–400 mg elemental magnesium/day	Sleep, cramps, anxiety, blood pressure	563	Solid base. The glycinate form is the best tolerated. Reduce the dose in kidney disease
Magnesium L-threonate	1.5–2 g/day of the compound (~144 mg elemental Mg)	Cognitive focus claim	4	The claim of crossing the blood-brain barrier better comes from an animal study. It costs several times more than the glycinate
Zinc + copper	15–30 mg zinc + 1–2 mg copper	Immunity, testosterone, skin	1.363	Broad base. Isolated, prolonged zinc causes copper deficiency — which is why they come together. Upper limit for zinc: 40 mg/day
Selenium	100–200 mcg/day	Thyroid, antioxidant	320	Narrow window. Upper limit 400 mcg/day; above that there is selenosis
Iodine	150 mcg/day (adult RDA)	Thyroid function	72	Excess can trigger thyroid dysfunction in people with thyroiditis. Not an item for high doses on one's own
Iron bisglycinate	25–50 mg/day	Iron-deficiency anemia	14	Only with proven low ferritin. The bisglycinate form causes less constipation than the sulfate
Boron	3–10 mg/day	Free testosterone, bone metabolism	13	Small studies. Upper limit 20 mg/day

Performance and muscle

Feature	Usual range	For what	RCT/meta	Caveat
Creatine monohydrate	3–5 g/day. Optional loading: 20 g/day in divided doses, for 5–7 days	Strength, power, lean mass, cognition	878	It is the best-studied sports supplement there is. It raises serum creatinine without kidney injury: warn whoever reads your lab results. No cycle or off period needed
L-glutamine	5–10 g/day	Recovery, intestinal barrier	207	The good evidence is in critically ill and burn patients, not in people who train
Acetyl-L-carnitine (ALCAR)	500–2,000 mg/day	Cognition, neuropathy, fatigue	173	Real base, above all in diabetic neuropathy. Raises TMAO, a marker linked to cardiovascular risk
Hydrolyzed collagen + vitamin C	10 g/day, with vitamin C, 30–60 min before training	Tendon, ligament, skin	234	High volume. Timing of the dose matters here, unlike most
Type II collagen (UC-II)	40 mg/day	Knee osteoarthritis	16	It is a different mechanism: oral tolerance, not raw material. Do not confuse it with the hydrolysate, nor add the doses together
Glucosamine + chondroitin	1,500 mg + 1,200 mg/day	Osteoarthritis	98	Much studied and still inconsistent — the case where volume did not settle the question. Glucosamine usually comes from shellfish: watch for allergy
MSM (methylsulfonylmethane)	1.5–3 g/day	Joint pain, inflammation	23	Modest base. Well tolerated, small effect when it appears

Sleep, mood and cognition

Feature	Usual range	For what	RCT/meta	Caveat
Melatonin	0.5–3 mg, 30–60 min before bed	Sleep latency, jet lag adjustment	773	Broad base, best for jet lag and phase delay. It is limited to 0.21 mg/day as a supplement. A lower dose usually works better than a high one
Glycine	3 g before bed	Sleep quality, body temperature	5	Only five. The studies are consistent and low-risk, but the base is thin — smaller than the reputation suggests
L-theanine	100–400 mg/day	Calm without sedation; pairs with caffeine	84	Decent base. The combination with caffeine is the one with the most data
Citicoline (CDP-choline)	250–500 mg/day	Attention, memory	44	Better backing than most over-the-counter nootropics
Alpha-GPC	300–600 mg/day	Choline for acetylcholine, strength	4	Four trials. One observational study raised an association with stroke, not yet confirmed
GABA	100–750 mg/day	Anxiety, sleep	11	Oral GABA crosses the blood-brain barrier poorly. If there is an effect, the mechanism is probably not what the label says
Inositol (myo-inositol)	2–4 g/day; 4 g in the PCOS studies	PCOS, anxiety, insulin sensitivity	87 (only in PCOS)	One of the best evidence-to-risk ratios on this page
Soy lecithin	1–2 g/day	Source of choline and phospholipid	18	Cheap source of choline; little demonstrated effect of its own

Longevity and metabolism

Feature	Usual range	For what	RCT/meta	Caveat
Coenzyme Q10	100–300 mg/day, with a fatty meal	Mitochondria, statin myopathy	657	Broad base. Absorption depends on fat taken with it. May reduce the effect of warfarin
Ubiquinol (reduced CoQ10)	100–200 mg/day	Same purpose, reduced form	included in the CoQ10 count	Better absorption claimed, above all over age 40. Costs more
Alpha-lipoic acid (ALA)	300–600 mg/day	Diabetic neuropathy, insulin sensitivity	65 (only in diabetic neuropathy)	Good base in the indication. The R form is the active one. May lower blood glucose — caution in anyone on antidiabetics
NAC (N-acetylcysteine)	600–1,800 mg/day	Glutathione, mucus, compulsive behavior	1.183	It is the precursor that works, while oral glutathione is poorly absorbed. In some countries it is a medicine
Quercetin	500–1,000 mg/day	Antioxidant, senolytic under research	355	High volume, modest clinical results. Low oral bioavailability. Inhibits CYP3A4
Resveratrol	150–500 mg/day	Sirtuins, metabolism	391	Almost 400 trials and the promise did not hold up — the clearest case of volume without results. Very low oral bioavailability
Fisetin	senolytic dose not established in humans	Senolytic	2	Two published human trials. The high-pulse protocols that circulate come from an animal study
Spermidine	1–6 mg/day	Autophagy, longevity	9	Base mostly epidemiological and preclinical
NMN	250–500 mg/day	NAD+ precursor	21	Raises NAD+; clinical outcome not demonstrated. The FDA removed NMN from the supplement category in the US in 2022
Astaxanthin	4–12 mg/day	Antioxidant, skin, eye	106	Better base than its niche reputation suggests. Fat-soluble carotenoid: take with fat

Gut and liver

Feature	Usual range	For what	RCT/meta	Caveat
Omega-3 (EPA + DHA)	1–3 g/day of EPA + DHA combined	Triglycerides, inflammation, cardiovascular	2.597	Huge base, strongest for triglycerides. Read the label by EPA+DHA content, not by capsule weight. High doses increase bleeding time
Multi-strain probiotic	1–50 billion CFU/day	Microbiota, digestion	5.248	The highest number on this page — and the most misleading: the effect is strain-specific and does not transfer. Caution in the immunosuppressed
Psyllium	5–10 g/day, with plenty of water	Fiber, constipation, cholesterol	216	Solid base. Without enough water, it causes obstruction. Keep 2 h away from other medications
Sodium butyrate	300–600 mg/day	Intestinal barrier, colonocyte	5	Thin base. The butyrate produced by fermented fiber probably yields more than the capsule
TUDCA	250–1,500 mg/day	Liver, cholestasis, endoplasmic reticulum stress	24	The evidence is hepatological, not for liver protection during an anabolic steroid cycle
Natural colesevelam	as labeled	Bile acid sequestration claim	77 (for the drug)	Confusing name: real colesevelam is a prescription drug. The over-the-counter product with that name is something else — check the actual composition first

What the count revealed

Resveratrol has 391 trials and still disappointed. It is proof that research volume is not synonymous with results — which is why the column gives the number, not a seal of approval.
Probiotics have 5,248, the highest on the page, and it is the most misleading, because the effect is strain-specific: the thousands of trials do not add up in favor of the bottle you bought.
Glycine, alpha-GPC, butyrate, fisetin and magnesium L-threonate have between 2 and 5 trials each. They are the five with the thinnest base on this page — and L-threonate, with 4, is the one most out of step with the price it charges.
No item was left without a count. The thirteen that were missing were closed, and three of them changed how the page reads: vitamin B12 has 436 trials, selenium has 320 and vitamin C has 270 — the three were among the best-studied items here and were showing up blank.
Supplement doses also have a ceiling. Selenium, zinc, iodine, B6 and vitamin D have a defined tolerable upper limit; exceeding it brings no extra benefit.

References

This page did not come from the secondary source. Every number was collected by me from the sources listed below, on September 4, 2026, and the query used is stated above.

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