The theory goes something like this: if you use legal drugs such as tobacco or alcohol, or even what some consider “soft drugs” like marijuana, you are more likely to slip down the slope to using “hard drugs” like amphetamines, cocaine and heroin, than people who never get started using soft drugs in the first place. The starter drugs are often referred to as gateway drugs because use of them is seen as the first step through the gateway to even more dangerous behaviors.