The discovery of penicillin G was one of the most significant findings of the 20th century and certainly one of the most important discoveries in modern medicine. Since the 1940s, the world has remained dependent on this safe and effective antibiotic, and it has been used extensively not only in human medical applications, but in animal and agriculture to enhance the growth of livestock. Such diverse applications have resulted in the global distribution of this antibiotic, and its dispersal into a wide array of environments. Moreover, penicillin G is known to degrade into immunogenic metabolites, which have been identified in various agricultural products and wastewater systems, fuelling much debate on the safety of the use of this antibiotic. Unfortunately, the overuse of penicillin G and other antibiotics has led to the rise of resistant organisms and ushered us into a new age of treating infectious disease. The rise in resistance associated with penicillin G and its ability to produce allergy inducing metabolites in animal and medicinal applications are deeply intertwined, creating a unique and complex set of public health issues which is the subject of this review. Penicillin G will likely be used for many years to come, thus new understanding and insight is needed to address these public health issues.