Could doxycycline help existing cystic acne that has already formed?

Some: True cystic acne usually requires isotretinoin, which is not for the faint-hearted or risk-free but is well worth it. You'll also need to manage your disease long-term; systemic Doxycycline plus topical benzoyl peroxide may be effective for severe disease. Never use an antibiotic as sole treatment for acne. Cystic acne will ruin a job interview and is a grave social handicap. I wish you the best.

Dr Paudel agreed