How much damage can 4 months of bulimia cause?

Depends on behavior: Bulimia usually involves vomiting or laxitive abuse or both. It can be fatal in extreme cases and certainly can cause lasting damage. Depending on frequency, it can mess up your teeth (acid from the stomach) and body (disturbed electrolytes damage the heart and kidneys. Seek treatment as quickly as possible not just because of that but also because early treatment is more effective.

Depends on severity: Bulimia may cause electrolyte imbalances that lead to heart failure, as well as esophageal & gastric ruptures, which may be fatal. Other medical complications include bone loss, osteoporosis, dehydration, kidney disease, anemia and low white cell counts, which lowers the immune system and creates vulnerability to disease and infection. Also, gum disease, tooth decay. Please seek help!