We are first introduced to it when Sartaj visits the Ashram. He drinks a red tea, lays down on a mat, and when he wakes up he's completely alone. The next time he ingests it (in pill form), he has a visceral experience, remembering the problems he had with Megha. Even Gaitonde goes through a smorgasbord of emotions while on it, remembering his father and consequently breaking down over finally being free of guilt.
So what do we know about gochi?
We know it brings deep-rooted memories and feelings to the surface. We know it can cause a kind of spiritual awakening inside your mind, wherein you go through a carousel of feelings, from euphoria to shame to acceptance. Both Sartaj and Gaitonde revert to instances in their past that involved personal conflict without resolution.
Going by these effects, gochi sounds most similar to the drug ayahuasca. This hallucinogenic brew from the Amazon is made by combining several plants, including Banisteriopsis caapi and Psychotria viridis - both of which have psychedelic properties.
The effects of the drug may vary from person to person, but it essentially makes you reflect on past experiences and alter your regular cycle of thinking. According to Healthline,
It gives one the strength to think about their traumatic past and confront those things that he usually pushes out of his conscious mind. Ayahuasca activates the amygdala - the region of the brain where early memories are stored, specifically those traumatic and most significant experiences like losing a loved one.
This sounds pretty much identical to what the people in the ashram experience. However, the drug is also shown as highly addictive, so what could the reason be for that?
As you might have noticed, Guruji and his associates want a degree of control over their subjects. The gochi drug they create keeps the people coming back for more, and they might have consciously made it highly addictive so their people could never leave.
They might have combined ayahuasca with a small amount of the drug PCP to make it highly addictive.
Phencyclidine, or PCP, is a synthetic drug that can cause an 'out of body' experience combined with violent behaviours. We already saw that Gaitonde went ballistic after consuming the gochi, and smothered Guruji. However, PCP is also highly addictive, and has very similar withdrawal symptoms to gochi.
PCP withdrawal can cause confused thoughts, increased cravings, anxiety, violent behavior hallucinations, suicidal thoughts and delusions.
That sounds exactly like what both Sartaj and Gaitonde go through. Sartaj becomes violent, confused, and even starts having delusions and hallucinations. Gaitonde straight up becomes suicidal and kills himself.