Anyone know how well cortisone injections work for cystic acne?

Local only: This can be used selectively for acute cysts but are only part of more comprehensive treatment with oral and topical medications. For severe cases Accutane which is used for 15-20 weeks can work well long term. Discuss with dermatologist your history and treatment options.

Cystic acne: I agree. Steroid injected directly into a cystic acne lesion can and does work well but is not always first-line treatment. It is more of an augmentive treatment to whatever baseline treatment a patient is receiving.