The first drag
A student new in college usually dips their toe in substance either because of curiosity upon seeing someone else, or on insistence of a friend / senior etc.
Most students say they took the first drag on a friend’s insistence. “I started doing it because of curiosity. My roommate would do it every weekend. One day, when he was rolling, he offered me and I thought I would try it. It’s a different high altogether and I got hooked,” says a student who hails from Kolhapur and is studying law. 
Senior invites you for a drink and then after a few days it goes to marijuana and eventually all the other drugs. Now some of my batchmates are also involved. 
Peer pressure has always been a big issue. In a lot of situations, a student dosen't get forced to dip themselves in substance upon someone else's pressurization. It happens only because the student himself forces himself by thinking that he might face pressurization in the future.
The fear of being left out from a friend circle makes a student unwantingly agree to things he would normally consider wrong.
It has been famously said that if one doesn’t want to go south, it is not enough "not to go to south". For south will eventually catch up with you. It is imperative thus to walk north. We are missing this very notion in our dealings with our college students. Are we reaching out to the individual behind the student? That is the burning question. 
For the longest time, we have swept this matter under the rug and not endeavoured to make individual students mentally resillient to the drug menace.
At the time of entering college, most students have the mindest that they are entering college to explore, extend their horizons, do new things, make experiences, expand network etc. In this rush of new goals, their morals and values get lost. They fail to understand that there are things which are better left out of their desire to explore or the instinct of curiosity. They fail to understand that "new things" do not have to involve damaging things. They don't know what kind of experiences they should make. They want to keep everyone possible on their network and fail to understand that certain people are better off not being on their network.
Having methods to remind students of their cultural identity and the harms of substance abuse is important at a time when their minds are too busy being lost in a jungle of incomplete advices.
The early starters problem
We see elder people smoking cigarettes or doing alcohol around us. Their lives aren't destroyed in the ways that are portrayed when we talk of addictions in college.
The sharp reason is that our previous generation started on these vices later in their lives, and even then they had the issue of availability.
In the current scenario, students have very easy access to any substance they wish to consume. Students in the pursuit of expanding network and gaining new experiences, have it very easy to visit new places and campuses, which expose them to more things that can derail them. They likely won't stop at a gateway drug. They curiosity, access and insistence leads them to try more things.
College students were twice as likely found to develop alcohol related and drug related disorders than the rest of the general population. 
College students start off at the age of 18 - 19. They have curiosity. They have incomplete guidance they get from the internet and spoil friends / seniors. They have 3 - 4 years in college to do uneducated experiments on them and try as many substances as they can. By the time they graduate, they are much susceptible to falling prey to greater vices in their life.
Misconceptions around alleged benefits
There is a set of students who justify their drug usage by pulling up claims that these substances help enhance creativity or helps them study better. 
These so called study drugs are double edged swords. While they may marginally improve performance for the couple of hours a student is high, it comes with much worse harms - including but not limited to addiction, drug reliance, mental/ medical/ psychological degradation, susceptibility to worse substances etc, eventually leaving their future hanging.
The extreme sides
The business is big, and even at big institutions like IIT-K, people are into drug peddling - including students, security personnel and temporary staff. 
As per last one-year data, 10 per cent of students were addicted to consuming ganja while 20 per cent of students had narcotic substances in their possession. 
When so many students are getting into uncontrolled drug consumption, it is not uncommon to hear of situations where students died because of drug consupmtion or acquired a chronic health issue.
There is a new entrant - New Psychoactive Substances. These are technically not illicit in the classical sense. These mimic the effect of existing classical drugs, but have sythetically modified chemical structures.
Manufacturers keep changing the chemical composition ever so slighty to stay ahead of the law and market their drugs as "legal".
Lack of critical research on these substances mean that there isn't heavy evidence against these substances. As a result, manufacturers and users of these substances claim that these have non existent damage.
The lack of regulation by authorities on these substances mean that these substances are easily available to students.
The same logic is used by students to justify their usage of this drug - that these drugs are not banned and there aren't strong evidences of its harms. The same reasons also manage to easily compell new students into these drugs, who get convinced that synthetic drugs aren't "bad" like classical illicit drugs.
But none of this means that synthetic drugs are legal or safe. Synthetic drugs are not quality controlled or regulated, so there are concerns over what are the ingredients in them. They are just new and it will take time for the regulatory authorities to catch up and spread awareness.
The issue will only rise. With prevelance of liberal mindsets and influences of cherry picked habits from other cultures, the stigma around substance abuse is declining among students. Normalcy is increasing and more students are falling prey.
It is important that students don't leave their individuality. They don't sacrifice their values. They don't give up their values and philosophies.
 Pune: 'One in five students doing drugs' : link
 Drug abuse in engineering hostels. : link
 Drug abuse in Indian colleges – time to change gear : link
 A study of substance abuse among male engineering students staying at hostels in a township near Kolkata : link
 IIT-Kanpur students are so stoned that it’s called in the cops : link
 1,200 engineering students caught searching for drug peddlers in Hyderabad : link
 Use of new psychoactive substances in educational institutions : link