The drugs work well at first but gradually lose their effectiveness.

这些药的效果起初非常好，但后来逐渐失效。

At first he was most dictatorial and aggressive in what he said,but when he realised that he would get nowhere by that means,he began to sing another tune.

起初他的说法十分专横武断,但当他认识到这样做行通的候,他就开始改弦易辙了。