Jack Gordon’s review published on Letterboxd:
A single character, observing the time and place around him very, very closely. A potent, well-conceived, thoroughly subjective experience. It achieves a great deal without troubling with the "why" or the "how", and seems to move itself along quite effortlessly. At many points, it could easily have become any film it wanted to become.
This sort of nervous ambiguity works so well in films, and really does pose all kinds of interesting possibilities when approached from within the tighter structures of more literal, story-driven works. Drug use here operates as a very palpable "unknown" for both the characters and the audience, and our shared confusion becomes the very essence of the film. This is what I think these late 60's/early 70's American films are doing so well: they're creating very, very ambiguous landscapes that mean so much, and so little, and that you get lost in. They're all about the process of change, and while The Trip is an extremely literal, pop-cultural example of this, it's plot really isn't so different from The Shooting, which sees a cowboy looking for something out in the desert before going even further out to find it. Pop-culture and genre seem completely interchangeable here, as what these films are really trying to get down to is the single shared narrative of a certain people, at a certain place, at a certain time. The ambiguity we think we're watching is actual ambiguity that we're feeling, and it doesn't leave us after the credits roll. These films are doing something right.