Deleuze on drugs and the plane of immanence:

The danger of drug use, and here Deleuze and Guattari are talking principally about the noetic danger (the social and the physical dangers are only alluded to) is to be stuck in « phantasy » separated from the plane of consistency (real life transformation). The secret is not chemical (material substances) but alchemical (noetic processes):

"drug users believed that drugs would grant them the plane, when in fact the plane must distill its own drugs"

The discussion on this point is noetic rather than medical, moralistic or empirical. On the empirical question Deleuze is quite clear: taking drugs ultimately leads us on the path of conformism, the cardinal virtue is abstention (not abjuration).

On the noetic question (but the two are intertwined), the aim is

"To reach the point where « to get high or not to get high » is no longer the question, but rather whether drugs have sufficiently changed the general conditions of space and time perception so that nonusers can succeed in passing through the holes in the world and following the lines of flight at the very place where means other than drugs become necessary. Drugs do not guarantee immanence; rather, the immanence of drugs allows one to forgo them (ATP, 286)."

The point is to « forgo » drugs in order to pass through the holes in the world and onto the lines of flight. Drugs, whether we have taken them or not, have changed our perception. They have allowed us to perceive the holes in the world, the gaps, the breaks, the cracks, the ruptures, the imperceptible fissures. However they do not allow us to take hold of the imperceptible and to become ourselves imperceptible:

"One does not conform to a model, one straddles a horse. Drug users have not chosen the right molecule or the right horse. Too bulky to grasp the impercep­tible and to become imperceptible, they believed that drugs would give them the plane (ATP, 286)."