n.a habit-forming drug that is not addictive but its use may lead to the use of other addictive drugs
英汉双解大词典
gateway drug(gatewaydrugs)
1.
N-COUNT（可数名词）
A gateway drug is a drug such as marijuana that is believed by some people to lead to the use of more harmful drugs such as heroin or cocaine. 诱导性毒品