Hi. Welcome. After hcg is mixed with bac water and stored in the fridge, it has a limited "shelf" life. Anywhere from 30-60 days. It can begin to lose potency within that timeframe or shortly thereafter. When you are given pre-mixed hcg, you have no idea when it was mixed or if it has been refrigerated. It's much better to receive freeze-dried hcg and mix it yourself. That way, you have complete control.