Toxicity refers to a drug’s potential to cause harm to a patient. While extremely toxic drugs are rarely approved for use, analyzing a drug’s safety is more complicated than determining whether or not it has any harmful side effects. Regulators must decide whether a drug’s benefits outweigh its potential harms. If a mild painkiller has the potential to cause long-term liver damage, for example, that would likely be deemed an unreasonable risk. On the other hand, a third-line cancer drug with the same potential side effect might be considered reasonably safe, due to the severity of the condition being treated.