Therapeutic agents are potentially toxic, for this reason, it is necessary to assess the toxicity of medicine to value the relationship between safety and efficacy. The therapeutic ratio is the relation between potency and toxicity. This relation expresses the parameter to evaluate the efficacy considering the potency, and the toxicity considering the safety. The pharmacokinetic parameters are adsorption, distribution, metabolism, and excretion are related to this criterion. The therapeutic ratio is the ratio between the maximally tolerated and the minimal effective dose of a therapeutic agent and it calculates divining the median lethal dose for the median effective dose. The therapeutic ratio considers the safety of the dose administrated. For instance, in cancer treatment, it represents the minimum tissue damage and the maximum tumour tissue killed. In therapy, the therapeutic ratio determines if a drug can be used on humans. Moreover, it hinges on the use of a drug if it is administrated drug chronically. It has a large therapeutic ratio, but its overall benefits are small. Drugs administrated against an acute disease have a low therapeutic ratio, but they have high therapeutic benefits.