Dawn
Great customer service
Great customer service! Quick to respond and very helpful. I absolutely LOVE the Zstack. I don’t want to ever be without it.
Response from Z-STACKJun 3, 2026
Thank you Dawn!

Zelenko Labs, built on the legacy of Dr. Vladimir Zelenko, creates products with purpose, precision, and integrity. Every formulation is made with high-quality ingredients and consistent standards, so you can feel confident in what you’re using. Thoughtful, reliable, and principled — Zelenko Labs products are made for people who care about quality.Our All American customer service team is here to help Monday through Friday, 9 AM to 5 PM EST — just give us a call at 1-800-ZELENKO (1-800-935-3656) or email our team at [email protected]
Z-STACK (zstacklife.com) has 95 customer reviews on Five Star Index, with an average rating of 4.1 out of 5.
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Personal Care · Orlando, Florida
Excellent

Personal Care · Grants Pass, Oregon
Excellent

Personal Care · Great Neck, NY
Excellent

Personal Care · Costa Mesa, California
Excellent
Showing 71 reviews with 5 stars · Clear filters
Dawn
Great customer service! Quick to respond and very helpful. I absolutely LOVE the Zstack. I don’t want to ever be without it.
Response from Z-STACKJun 3, 2026
Thank you Dawn!
Karen C.
I had an order "swap products" question this weekend and sent off an email asking how to do it! Well, I figured it out myself, made the swap, it was a quite easy actually. There was an email from the Z-stack customer service department in my inbox this morning, that was quick! We went over the details of my account and order, all was well. Been with Dr Zelenko for several years now, great products, great company!
Response from Z-STACKJun 2, 2026
Thank you Karen!
Daniel D.
Choosing some of my supplements from Z stack may have been one of the best choices I made in years for my health. The vitamins I choose to use are the z stack with vitamin c, d, zinc and quercetin. Prior to these vitamins, I would take just vitamin c and d. I have learned so much from Dr Zelenko during the COVID times, I really didn’t trust many drs at the time but he was true to his word, may he Rest in Peace. This company is legit if you want your immune system working well, in my opinion, the company works with you and the delivery is pretty fast. I really do appreciate this company still existing and I pray they continue.
Response from Z-STACKMay 27, 2026
Thank you Daniel!
Marie L.
I have been taking this for many years in fact since it came out. I have not gotten sick and I truly believe it is because I take this every day. I have it on auto ship so I am never with out it.
Response from Z-STACKMay 18, 2026
Thank you Marie!
Lisa R.
This company is always there to help whether it’s adding a bottle or skip a month. Thank you for your outstanding service
Response from Z-STACKMay 18, 2026
Thank you Lisa!
Roy C.
Customer service is everything !!! I credit Zelenko for providing courteous, timely, professional customer service from start to finish. The product is #1 in my experience during COVID epidemic. I continue using the product faithfully. Opting -out from taking the vaccination was 100% due to my faith in GOD and the product living up to its' claims to strengthen my immune system ! To date, I have not been disappointed and commend Dr. Zelenko for developing his outstanding formula. GOD bless him!
Response from Z-STACKMay 1, 2026
Thank you Roy!!
Giuliana H.
Thank you so much for the quick response, for the product that is beneficial for our health, and for your help also on sending us the vitamins to our current address. We truly appreciate it and value your business.
Response from Z-STACKApr 23, 2026
Thank you Giuliana!
Donna S.
This is my first year since Covid to be and feel healthy even during flue season. The Zelinco Protocol is a wonderful solution for rebuilding your immune system.
Response from Z-STACKApr 17, 2026
Thank you Donna!