I take the medicine once every four hours. OR I take the medicine every four hours. Which is correct? Thanks.?

我認為 I take the medicine every four hours. 每四小時服藥較合理，加了once除非有对照別的服藥方式，可能有些藥是每四小時服藥两次(含)以上，那麼再使用，否則就是贅字了

dosage=the amount of a medicine that you take at one time=once="at one time"
Never exceed the recommended dose (once or twice,or thrice-adv.---used three times) of low dose at one time=once=once every four hours=each taken "every one" every four hours=1x4 on the prescription.

I took the medicine every four hours.動詞時態用「簡單過去式」比較合理。
1. take是action verb,有發生的時間點，所以我們講已經做過的事情時，要用「簡單過去式」。服藥如果尚未發生，用「簡單未來式」。I will take the medicine every four hours.如果是「習慣」，一直都是如此做，才用「簡單現在式」。但長期藥物通常是按日服用，每四小時服用一次，好像有點奇怪。什麼病會服藥這麼頻繁？會睡眠都要受影響。

2. 強調每四個小時，服「一次」時，才加上once。

I take medicines daily at every four hours.

I take the medicine once every four hours