gateway drug
noun [ C ] uk/ˈɡeɪt.weɪ ˌdrʌɡ/ us/ˈɡeɪt.weɪ ˌdrʌɡ/
入门毒品，上钩毒品（诱使吸食者服用危险性更强的其他毒品）
a drug whose use may make it more likely that someone uses other, more dangerous, drugs
Early intervention could prevent adolescents from "graduating" from so-called gateway drugs such as alcohol and marijuana to harder drugs such as meth. 早期干预可以防止青少年从酒精和大麻等所谓的入门毒品 "发展"到冰毒等更具危险性的毒品。
“敲门砖”，引子
something that makes you more likely to try other things that are similar but more unusual or difficult
Stephen King was my gateway drug to serious literature. 斯蒂芬 · 金的作品带领我进入了严肃文学的殿堂。