Ultra-powerful supplement and as always, Dr Mercola does an amazing job on quality. As mentioned in the Quercetin & Pterostilbene review, this zinc mixed with Quercetin & Pterostilbene along vitamin C are ready to kill anything we have dealt with. We always take the blend of supplements as we start to feel sick, and results have been great, especially during flu season. It has either killed the sickness all together or drastically shortens the duration without having to take antibiotics. Great product, even better when paired with the other two. I highly recommend.