When Susanna starts gnawing at her hand in Chapter 23, Valerie, one of the nurses, administers her Thorazine to calm her down. Kaysen recalls the experience using a paradox and a simile:
“Oh, Valerie,” I said, “you promised—” Then the Thorazine hit me. It was like a wall of water, strong but soft.
Thorazine is a powerful antipsychotic given to many of the girls in the ward when they are deemed to be "acting out." Kaysen writes often about how the drug had a habit of sapping patients of their personalities, reducing them to shells of themselves.
Susanna feels betrayed and powerless when Valerie gives her Thorazine despite promising she wouldn't. The simile "like a wall of water" describes the uncontrollable, all-consuming power of the drug and how she feels as though it threatens to drown her. "Strong but soft" is a paradox, communicating that the drug is both harsh (because it acts as an unstoppable force) and gentle (because it makes the world and one's thoughts less sharp).
These devices work together not only to describe the patients' experiences with medicine in the ward, but also to emphasize the overall feeling of powerlessness Susanna and her fellow patients feel. Just as Thorazine can take over the body, McLean and Susanna's diagnosis have taken over her life.
In Chapter 23, Kaysen uses the following paradox to describe her time at McLean:
For many of us, the hospital was as much a refuge as it was a prison. Though we were cut off from the world and all the trouble we enjoyed stirring up out there, we were also cut off from the demands and expectations that had driven us crazy. What could be expected of us now that we were stowed away in a loony bin? The hospital shielded us from all sorts of things. We’d tell the staff to refuse phone calls or visits from anyone we didn't want to talk to, including our parents.
The paradox here is the idea of McLean being both a "refuge" and a "prison," as a refuge is a place of peace and safety while a prison is a place of fear and control. By describing the hospital in this way, Kaysen is communicating that the hospital's impact was complex; while it offered protection for patients struggling with their mental health, it also often exacerbated their difficulties by dehumanizing them and stripping them of freedoms. The patients are protected because they're under close watch, but they're also cut off from the outside world and feel powerless.