Z-STACK Avis 

Dr Zalenko's products are top of the line; my husband and I have been on them since the onset. We have also shared them with family and friends for them to try. We feel our immune system has gotten stronger since we first started with Z-stack and now on Z-detox. I will continue to promote them on facebook and instagram as well because I trust this for everyone.

At first I couldn’t understand what you were trying to tell me, but then did. All messages were in a calm and friendly tone. Thank you very much for your attention and support.

I had not gotten my order after 2 weeks time. I was sent a replacement right away. Thank you! Also, this product-Z-Stack has been fantastic in maintaining immune system. I have been taking it for years and have not gotten sick for a long time. No yearly cold or flu like many acquaintances. Highly recommended.

I am very fortunate to have found Dr Zelenko’s vitamins. At 80 years old, I have been able to stay well and have not suffered even one Covid event. I attribute my good health to Dr. Zelenko’s vitamins.

I had a fast and great response to my issue that was quickly resolved.
I am so thankful!
Pam

I get the kids gummies for my children and end up stealing some for myself

Been using Z-Stack and Z-Night and really like both. Z-Stack feels like solid daily support, and Z-Night helps me relax and sleep better without feeling groggy. Clean formulas, all natural, brand I trust. Would recommend.

Zstacklife has been full of contradictions, gaslighting and evasive customer service. They sent my shipment confirmation at 1:16 PM, only a few hours before closing. I didn’t see it until after they were closed, and when I called the next morning, they said it had already shipped and refused to cancel.
When I brought up the late confirmation, the rep denied the timing despite the clear timestamp. When I emailed support with the screenshot, they dodged the issue entirely and blamed a credit card problem that wasn’t even relevant. My online account also marked the order as “Ready for pickup,” which is odd for an online-only business.
The most concerning part? Instead of addressing my questions or correcting the issue, the company cancelled my subscriptions. A transaction like this is akin to a toddler throwing a tantrum, but a health company to shut down the conversation rather than resolve it is inexcusable.
This is extremely toxic, dismissive, and unprofessional.

I've been taking Z-Stack for close to 4 years and have not been sick one day since I started taking it. I am 72 years old, and full time daycare for a granddaughter in school so the germs do come home, but she also has not been sick since she started taking the Kid's Z-Spike gummies. I DO NOT understand all the bad reviews unless they are bots or angry people in general. I have needed to contact customer service MANY times and always (during business hours) get a live person with NO foreign accent, and they are always more than helpful! For those who are having problems with customer service, perhaps you're calling a wrong number. Their customer service # is 800-935-3656 and I NEVER have an issue with getting a wonderful representative. The product itself is a godsend. Miraculous to NEVER get sick at 72 years old in the 4 years I've been taking it. IGNORE BAD REVIEWS! Not true!

Couldn’t tell if this product helped or not with immunity issues. What I can say is that if you get a subscription, it’s not that easy to stop it. It is common these days I guess to get no customer service and finding a place to submit a request or complaint is a lot of fun. I have combined bottles to make room in my cabinet but still have seven bottles… when you think you have cancelled … guess again.

I started taking Z Stack as part of Dr. Zelenko's prophylactic Covid protocol, as soon as it became available. I am unvaxxed, did NOT get Covid and did not get any flu or respiratory infection. I'll take these as long as they are available.

Not sure what is going on with this company, but it is not good. After I placed an order for 2 bottles of Z-Flu on 04/30/25, they sent an e-mail on 05/08/25 saying..."We’re reaching out with an important update about your recent order for Z-Flu.Due to an unexpected backorder, we’re currently unable to ship your Z-Flu bottle as scheduled. We sincerely apologize for the inconvenience and are working hard to resolve the issue as quickly as possible". I have sent NUMEROUS e-mails telling them to refund my money to my credit card. Today is 05/15/25 and they have still not refunded my money! This is not the first time this company has not fulfilled my order, but I thought I'd give them one last try. NEVER AGAIN! BUYER BEWARE!

Does anyone else's Zstack smell/taste like stink bugs? I've been getting this product for years and it never smelled like this! I've actually gotten sick/upset stomach, so have to stop taking it.
I too, have had issues with getting my purchases timely and noticed that you cannot remove/delete credit cards that you put on file. I've referred family & friends to this product but no more!

I’ve been using Z-stack and Z-Flu for 3-4 years now and liked it. From my experience their customer service has become horrendous! In the past you could speak with a real person. Not anymore. It’s all automated via email only. I’m still waiting on an order from their Black Friday sale November 28th! Another two orders from December and January also. They keep saying “shipping tracking numbers going out this week.” But it never happens. Right now I’m out nearly $160 and I have a bad feeling they are blowing me off. If I ever get my order, I will not purchase anymore. I use to recommend their products, but now I’m embarrassed that I did. Use caution when ordering.

I've been taking 2/daily Z-Stack (monthly auto-ship) since hearing Dr Zelenko speak several years ago. I am a frail 85# 75 yr old with advanced COPD/Bronchitis that has not had so much as a cold or a flair-up since & still going strong. Prior, I would have 3-4 severe, lengthy flair-ups annually. It's been a blessing for me.

Absolutely horrible service

I have been charged twice and not received my kid's vitamins. They charged me once for an order I didn't place. I received a terrible quality product in the summer months that looked like it had melted during shipping. Definitely do NOT do business with this company.

Good products but their customer service is the absolute worst!

We received kids products that were not as advertised nor what we had received in prior orders. I asked for replacement products to be sent. They want me to pack up the products received, mail them back and pay for the shipping! Totally ridiculous!

Not how you run a successful business and want to keep returning customers!

Customer service is the worst. The label was created, but never received by the post office. When I got Larry on the phone, he blamed the post office. No response to emails. I will notify my credit card company to get my money back. Do not do business with this company! They simply do not care and probably over priced?

ordered a bottle, but there's no order confirmation and ship tracking. nothing happened except a ad email regarding next purchase. it's been a week and i still get nothing.

i would avoid this site forever and don't order anything from there!

I had been purchasing various supplements from Zstack. They were my go to and I trusted this company. My most recent purchase (a few months ago) included the kid's gummy supplements along with my usual order. The regular order was fulfilled with the exception of the kid's gummies. Initially, I did receive a mass email that explained issues getting the gummies out but they had a fulfillment date. With that, I decided to order more gummies to stay ahead of future issues. That fulfillment date passed a while ago and I've contacted them twice with no response. If they ever fulfill my orders, I will cancel my account with them. For now, my trust in them is gone and I will never buy another product from them again. Receiving no response to my concerns is not acceptable.