What would happen if i use lymecycline long term?

Doctor's supervision: I believe it is always best to take medications under the proper supervision of a doctor. This goes especially for antibiotics. The antibiotic you mention belongs in the tetracycline class, and can have side effects which include rash, headache, diarrhea, nausea, vomiting, dermatitis, dysphasia, liver problems, even esophagitis among others. Hopefully you can see an ID doc for help.