The ZStack vitamin formula by Dr. Vladmimir Zelenko, MD is touted to be general health and “all-in-one immune boosting super formula that is made in America and is both Kosher and GMP-certified. The supplement has a popular appeal among those trying to avoid getting COVID but in this review, let's focus on the ingredients in the Z-Stack vitamin combo, the research, potential side effects, and things to keep in mind if you decide to buy this supplement.
What Is a Stack?
In the dietary supplement world, a stack refers to combinations of nutrients that when used together are said to work together to enhance and magnify the effects of each other in order to generate greater benefits. There are many popular supplement stacks you may have heard of such as these:
| Supplement Stack | Proposed Benefit |
| arginine and L-citrulline | raise nitric oxide levels |
| vitamin B6, zinc, and magnesium (ZMA) | raise testosterone/ help with sleep |
| ephedrine, caffeine and aspirin (ECA) | speed weight loss |
| protein and carbohydrates | increase protein assimilation |
| arginine and ornithine | raise HGH levels |
The proof of effectiveness for various supplement stacks fluctuates depending on what is being discussed, so it's always wise to validate the evidence for yourself.
With Z-stack vitamins, the ingredients are supposed to enhance the effectiveness of the immune system to battle infections. While not explicitly stated by the company, many in the public believe the supplement helps with protection from COVID-19. This may be related to research conducted by the supplement's inventor, Dr. Vladimir Zelenko.
Who Is Vladimir Zelenko MD (November 27, 1973, to June 30, 2022)
Vladimir Zelenko was a family physician in New York who was the originator of the Zelenko protocol, a Covid-19 treatment consisting of hydroxychloroquine (HCQ), zinc sulfate, and azithromycin. In at least one study, the Zelenko protocol, along with intravenous vitamin C, lead to speedier recoveries after covid infection. He is also the author of Metamorphosis an autobiographical book that chronicles his journey of self-discovery. Loved by his patients and many others, Dr. Zelenko, unfortunately, passed from lung cancer in 2022.
Z-Stack Vitamin Benefits
According to the company, this is an overall immune health supplement. Here's a quick video the company posted about the supplement
Z-Stack Vitamin Company Information
The company is called Zelenko Labs LLC. Bottles of Z-Stack state that the supplement is “manufactured for” Zelenko Labs and the address listed is 17 State Street Suite 4000 NY 10004. This address corresponds to a large 42-story building in lower Manhattan. The building even has its own Wikipedia page. It is not known if this is the location where the supplements are manufactured. Another company address is 9045 La Fontana Blvd suite 105 Boca Raton, FL 33434.
Z Stack Vitamin Formula Supplement Facts Ingredients
Two capsules contain the following nutrients:
| Amount | Percent Daily Value | |
| Vitamin C (ascorbic acid) | 800 mg | 889% DV |
| Vitamin D 3 (cholecalciferol) | 125 mcg (50000 IU) | 625% DV |
| Zinc (zinc sulfate) | 30 mg | 273% DV |
| Quercetin | 500 mg | N/A |
A bottle contains 60 capsules so it will last you a month if you take two capsules per day. If you take just 1 capsule a day, then the dosages are as follows:
- Vitamin C: 400 mg
- Vitamin D3 62.5 mg
- Zinc: 15 mg
- Quercetin 250 mg
ZStack is a pretty clean supplement with not many other ingredients. The only inactive ingredient listed on the Supplement Facts label is hemicellulose which is used in the capsule. The supplement does not contain controversial ingredients such as silicon dioxide, carrageenan, or magnesium stearate.
With the exception of quercetin, the ingredients and dosages used in the supplement are similar to the Covid treatment protocol that Dr. Zelenko recommended for low-risk individuals, defined as patients who were younger than 45 with no other health problems and who were clinically stable.
Where Do The Ingredients Come From?
These days, many supplement ingredients come from China. When I reached out to the company I was informed the ingredients in the Zstack formula are sourced from the united states, mostly from Florida.
How Do You Take Dr. Zelenko's Vitamin?
The company recommends taking 2 capsules once a day with food. The company does not appear to specify the best time of day to take the supplements.
Vitamin C 800 mg
The RDA for vitamin C (ascorbic acid) is 90 mg a day for men and 75 mg a day for women. Vitamin C's reputation as an immune system enhancer dates to at least the 1980s. Linus Pauling, the only scientist to be awarded two unshared Nobel Prizes was probably the most popular academic to advocate mega-doses of vitamin C for things ranging from the common cold to cancer. In one review of the science, vitamin C supplements appeared to reduce the duration of cold symptoms by between 8% and 14% in adults and children respectively.
Studies revealing positive results with the common cold have used between 1000 and 2000 mg per day. While encouraging, keep in mind not all studies show vitamin C helps with cold and flu symptoms. For example in one such investigation, 3000 mg was shown to be ineffective.
Intense exercise, such as running a marathon, has been documented to reduce immune functioning and trigger cold/flu about one or two weeks after sporting events. Some research reveals vitamin C appears to prevent declines in white blood cells called lymphocytes after long-duration physical activity. In theory, this might improve resistance to infections.
Since it takes 250 mg to 500 mg to saturate the blood with vitamin C, the dosage used by Z Stack vitamins is more than adequate for most healthy people's needs.
Vitamin D3 125 mcg (5000 IU)
While more truly called a pro-hormone, vitamin D, which is derived from cholesterol, is important for a wide range of effects that go beyond its deficiency syndrome, known as rickets (weak bones in children). As proof of its diverse actions, each f the 40 trillion cells in your body has receptors for vitamin D. This includes immune cells like T cells, B cells, and macrophages. This fact may be related to preliminary research showing vitamin D supplements may protect against the influenza virus.
The vitamin D in Dr. Zelenkos's supplement is cholecalciferol (vitamin D3) which the same form as made from sunlight and found in animal products like egg yokes. Some feel this is superior to vitamin D2 (ergocalciferol) which is derived from yeast.
Whether vitamin D helps people who have Covid-19 infection is controversial. Some research appears to show more serious infections in those who are deficient in vitamin D, but other studies show being deficient does not raise your risk of becoming infected.
This means more research is needed to elucidate the effects of vitamin D and coronavirus infection. For now, the best overall thing that can be said is don't become deficient. For most people, a supplement can prevent this. While blood tests usually designate deficiency as less than 20 ng/ml and normal levels of at least 30 ng/ml, the optimal, level of vitamin D for different health problems is not agreed upon.
Zinc Sulfate 30 mg
It's estimated that at least 30% of people worldwide may be deficient in zinc, a mineral with an RDA of 8 mg per day for women and 11 mg per day for adult men. Older folks may be particularly at risk of deficiency due to reduced appetites and the use of medications such as water pills and blood pressure medications like ACE inhibitors that can reduce zinc levels in the body.
Zinc has been well known immune mineral for many years. Decades ago, research revealed that throat lozenges, containing zinc gluconate shortened the duration of the common cold by about 33%. This has led to over-the-counter products such as Cold-Eeze which have become quite popular during cold and flu season.
Preliminary studies also revealed that zinc inhibits the replication of coronavirus in isolated cell cultures. Other research shows that zinc, used in combination with copper and polyphenols inhibits the replication of not only coronavirus but also viruses that cause influenza A and others that cause upper and lower respiratory tract infections.
In one meta-analysis, where researchers looked at 5 previous human trials, zinc supplementation was associated with 43% lower risk of dying from COVID-19 compared to those not using zinc supplements.
Quercetin 500 mg
Quercetin is a flavonoid, a type of plant nutrient that confers health benefits to humans. While the nutrient has no RDA, various studies have revealed this antioxidant flavonoid, raises nitric oxide levels and reduces inflammation, blood pressure, and bad, LDL cholesterol. Foods and beverages that contain quercetin include apples, onions, broccoli, kale, cauliflower, turnips, brussels sprouts, green tea, peanuts, shallots, tomatoes, grapes, and red wine.
Preliminary research suggests -at least in a test tube – quercetin has antiviral effects, inhibiting the replication of viruses that cause polio, hepatitis,
SARS, and even HIV. Keep in mind, clinical studies involving humans have not yet confirmed these effects.
Dr. Zelenko was an outspoken proponent of using hydroxychloroquine for covid treatment. Since prescription medications are not permitted in supplements, quercetin may have been used in Z Stack as a natural alternative to hydroxychloroquine. As reported by the Catholic Business Journal, quercetin could act in a similar – albeit weaker fashion -as hydroxychloroquine – in helping zinc to attack the virus. As Dr. Zelenko himself has stated, both quercetin and vitamin C are used as a “zinc delivery system.”
How Much Do Z-Stack Vitamins Cost and Where Can You Buy Them?
Here are prices listed on the companies website when this report was created:
- 1 bottle: $55 (about $0.92 cents per capsule)
- 6 bottles: $300 (about $0.83 cents per capsule)
- 12 bottles: $540 (about $0.75 cents per capsule)
If you choose to subscribe and receive automatic shipments, you will save 10% on all orders. All supplement purchases come with free shipping for those living within the continental united states. Dr. Zelenko supplements can be purchased directly from the ZStacklife.com official website, which may also have discounts and coupons.
Is ZStack Sold on Amazon?
At this time it does not appear the supplements are sold on Amazon or at local stores like Target, Walmart, Kroger, GNC, Vitamin Shoppe, Costco, Sam's Club, CVS, Walgreens, or Rite-Aid. Knockoff, imitation brands from other companies containing the same vitamin combination may be found on other websites such as eBay.
Does Z-Stack Vitamin Have Clinical Research To Back Up The Claims?
Technically, the company does not make any specific claims about what the supplement does. The Zstacklife website does state the formula was specifically designed by Dr. Zelenko who it's said after careful examination, put together this all-natural formula for supporting the natural defense system of the body. The supplement appears to be based on the Zelenko protocol with quercetin replacing hydroxychloroquine. Human clinical studies proving the supplement augments or improves immunity or reduces or mitigates infections however could not be located.
Can You Make Your Own Z Stack Supplement?
To the credit of the company, the dosages of each ingredient are listed on the Supplement Facts label. So, for those who believe in this supplement stack but want to try to save a little money, here are the ingredients, dosages, and prices from well-known supplement companies found on Amazon:
- Vitamin C 1000 mg $10.24 (100 caplets)
- Vitamin D3 5000 IU $8.09 (100 softgels)
- Zinc 50 mg $9.99 (250 capsules)
- Quercetin 800 mg $17.71 (120 capsules)
Purchasing all of these would total $46.03 which is a bit less expensive, than Z-Stack, which retails for $55. When supplement shopping also consider and investigate that the brands you choose may vary in quality. Notice that the dosages of each ingredient above are not exactly the same as those found in Zstack vitamins. The goal of this experiment was to balance prices with what well-known companies were offering.
Zelenko Labs Better Business Bureau Rating
The company did not have a BBB file or customer complaints listed at the time this report was created. It's not known if the company is accredited by the Better Business Bureau.
What Does Trust Pilot Say about Z-Stack Vitamins?
TrustPilot gave the Zstacklife company 2.6 out of 5 stars when this report was last updated. There were 12 reviews listed from customers with 17% giving the company a 5-star rating and 66% giving the company a 1-star rating. This will likely change over time so see the TrustPilot file for more insights.
Any Problems With FDA or FTC?
No warning letters from the Food and Drug Administration (FDA) or Federal Trade Commission (FTC) were discovered with respect to either Zelenko Labs or the supplements they make. This is good as it indicates the company is in satisfactory standing and working within established US government dietary supplement guidelines.
Z-Stack Vitamins Customer Complaints
Here is a summary of some of the customer complaints listed on the TrustPilot website:
- Allergic reaction after taking the supplement: watery nose congestion and runny eyes
- Never received supplements after ordering
- Took about a month for the supplements to arrive
- Unauthorized charges to credit card after ordering
- Difficulty reaching customer support
- Trouble canceling recurring orders
Keep in mind these complaints are from people leaving reports on only one website and may not represent others who are pleased with their purchase. To counter these, the Zstacklife website features testimonials from several satisfied customers.
Z-Stack Vitamins vs. Z-Flu Supplement
Z-Flu is another supplement sold by Zelenko Labs. Both supplements share common ingredients. For those wondering how they compare to each other, here are the ingredients side-by-side.
| Z Stack (2 capsuels) | Z Flu (2 gummies) |
| Vitamin C 800 mg | Elderberry extract 175 mg |
| Vitamin D3 5000 IU | Vitamin C 200 mg |
| Zinc 30 mg | Vitamin D 3 4000 IU |
| Quercetin 500 mg | Zinc 6 mg |
| Quercetin 100 mg |
The Z-Flu supplement also contains purified water, pectin, sugar, tapioca, citric acid sodium citrate, bitter blocker, flavor, and beet juice.
Note: a bitter blocker – not to be confused with beta-blockers – is a substance that blocks the mouth and tongue from detecting a bitter taste. Examples of bitter blockers include Adenosine 5′-Monophosphate and Homoericdityol sodium salt (HED).
Z-Stack vs. HemoHim What's Better?
HemoHim is a popular blood and immune system energizer supplement that contains various vitamins and herbs such as Angelica Gigas. The ingredients differ greatly from Z-Stack and while there is some research on HemoHim, there are no studies comparing these supplements to each other.
There is likewise a lack of research comparing the Z stack formula to Carnivora, another very popular immune defense supplement that is based on an extract from the Venus Flytrap plant.
How Long Does It Take To Recieve Z-Stack Supplements?
The company takes shipping very seriously. All orders include free shipping for those living inside the United States. Supplements are shipped Monday through Friday and if your order is received by 4 pm EST, the supplements are shipped to you the same day. You will receive UPS tracking information when the order is processed. The company ships throughout the continental US and to other countries also. While delays after supplements leave the warehouse are possible, it normally takes 3 to 4 days for the supplements to arrive at your home.
If you live in Alaska or Hawaii, your supplements may take an additional 3 to 4 days to reach you. Zelenko Labs also ships internationally to Canada and other countries. You can choose your country from the drop-down menu when you are ordering. International orders may require an additional 6 to 12 days to reach their destination.
Zelenko Labs Refund and Money Back Guarantee Policy
Zelenko Labs has a very stringent return policy. There are no returns. As stated on their website, their refund policy is “All sales are final. We will not provide refunds or accept returns.” Consider this when making a purchase.
Z-Stack Vitamins Side Effects, Adverse Reactions, and Contraindications
The supplement is expected to be safe in generally healthy people with no confirmed negative side effects. The general warning that appears on the supplement label reads as follows: “intended for use by adults 18 years of age and over. Do not use if the seal under the cap is broken or missing. Please consult your healthcare practitioner before taking and when using this supplement. Keep out of reach of children. Quercetin should not be used if nursing or pregnant.”
Side-effects statements like this are pretty standard on supplement labels. The part of the warning that may stand out to most people is women who are pregnant or breastfeeding should avoid quercetin. This caution may be because of the lack of clinical research involving pregnancy and quercetin supplements.
Other potential cautions and things to keep in mind when taking this supplement include:
- Start with less than recommended for the first week
- Stop taking or cut back if you experience nausea or stomach pain.
- Zinc may cause you to have a metallic taste in your mouth
- Stop taking Z-Stack at least 2 weeks before surgery unless your doctor tells you otherwise
- High levels of zinc may interfere with copper absorption. In theory, this might reduce immune function. However, there are no reports of this linked to the Z stack vitamin supplement.
- Vitamin C increases iron absorption. Those with hemochromatosis (iron overload disease) should use caution.
- Quercetin might lower blood sugar levels. In theory, those with diabetes may want to consider this.
- Animal research suggests quercetin given during pregnancy results in increased iron storage and inflammation in offspring during adulthood. This has not been confirmed in humans.
- Consider that other supplements you take may also contain vitamin C, vitamin D, and zinc
Z Stack Pros & Cons
| Pros | Cons |
| No proprietary blends | No peer-reviewed research on supplement |
| Ingredients have some proof | Awful return/refund policy |
| Manufactured in America | Not proven to prevent colds/flu |
| No confirmed side effects |
My husband and I have taken Z-Stack since the beginning of the Covid-19 pandemic in March 2021 and have not had covid. For the first 18 months we were taking 2 capsules per day then blood tests revealed our Vitamin D levels was way too high so cut back to only 1 per day. Still covid free to date, although most of our vaccinated friends are now getting covid for the second time. As a matter of interest, is there a study to show how successful Z-Stact has been I preventing covid over the past 3 years?
Thank you in advance,
Barbara-Ann McCarthy
Hi Barbara-Ann, I don’t recall seeing any Z-stack covid infection studies going out 3 years. Would be really interesting to know, wouldn’t it? Glad to learn you and your husband are both doing well and are Covid free!
Thanks for the in depth review. I was not familiar with the Z Stack Brand. Personally, I would not take a supplement with ephedrine, caffeine or aspirin; I’m assuming this was listed as a typical immune stack supplement. My husband is being careful to avoid supplements with arginine. He has been suffering with post-herpetic neuralgia for many months and read that arginine can be an issue.
Hi Judy, the z stack supplement doesnt contain ephedrine. I used the ephedrine caffeine and aspirin combination as an example of a supplement stack. for those not familiar with what a stack was, I was giving some examples along with their proposed uses. The ingredients in z-stack are a little further down in the review.
Definitely, your husband should avoid arginine supplements. Lysine appears to inhibit that virus from replication.
Another great review! Thanks so much for sharing your incredible science backed knowledge on supplements, I always feel like I learn so much reading all of your reviews Joe!
Thanks so much for saying that April! I appreciate you so much 🙂