If you're talking about emotional release:
* Suppressed: Holding emotions in, not allowing for release.
* Bottled up: Similar to suppressed, but with a sense of being tightly held in.
* Repressed: Pushing emotions down unconsciously, preventing them from surfacing.
* Stuffed: A colloquial way of saying someone is holding back their emotions.
* Claustrophobic: A sense of being trapped and unable to express oneself.
* Suffocating: Feeling overwhelmed and unable to breathe emotionally.
If you're talking about the purging effect of a cathartic experience:
* Constipated: Similar to bottled up, but specifically for emotional expression.
* Stagnant: Lacking movement, flow, or change.
* Unresolved: The emotional issue hasn't been addressed or worked through.
If you're talking about the purging effect of a cathartic experience in the context of art:
* Uninspired: Lacking the motivation or drive to create art.
* Unoriginal: Lacking creativity and originality.
* Staid: Formal, conventional, and lacking in spontaneity.
Ultimately, the best opposite of "cathartic" will depend on the specific context and how you are using the word.