The purpose of this invention is to provide hydrogel contact lens capable of releasing sustained drugs that is able to release anionic drugs, such as therapeutic drugs for allergy, effectively and mild-irritatingly while curing eyesight.The purpose will be achieved by providing hydrogel at least consisting of ionic monomers including both cationic and anionic monomers, in which the proportion of the ionic monomers is 5 mol %~20 mol % of the total amount of the monomers composing the hydrogel, and the content of the anionic monomers to the cationic monomers is 15 mol %~25 mol %.本發明目的在於提供藥物徐放性水凝膠隱形眼鏡鏡片,可進行視力矯正並且徐放低刺激且有效的過敏治療藥劑等陰離子性藥劑。此目的係藉由提供一種水凝膠來解決,其中,該水凝膠係至少由陽離子性單體及陰離子性單體之離子性單體構成,其中該離子性單體之構成比率,相對於構成該水凝膠之單體總量而言,係在5莫耳%以上20莫耳%以下,該陰離子性單體的含量相對於該陽離子性單體而言,係在15莫耳%以上25莫耳%以下。
