Answer:
Gateway Drugs
Step-by-step explanation:
Gateway drugs are drugs that are literally drugs that are a gateway, or commonly lead to further drug use of more dangerous harmful drugs. Examples of gateway drugs are things such as cannabis, or prescription drugs(getting addicted by taking to many, or continuous use even after there is no longer a need for the drugs).
Synthetic drugs are yes illegal, but they are already more hardcore drugs that have more damage than just cannabis.
Illegal drugs are the drugs that are illegal, such as those sold on the street or in big time businesses that aren't cannabis.
OTC drugs, are just over the counter drugs that you can buy at a local pharmacy.
-Hope this helped & Happy Holidays!