For therapeutic drugs, it refers a drug’s lack of “nuisance side effects,” side effects that are thought to have no long-term effect but that are unpleasant enough to the patient that adherence to the medication regimen is affected. The extent to which a drug’s adverse effects impact the patient’s ability or willingness to continue taking the drug as prescribed. These adverse effects are often referred to as nuisance side effects, because they are generally considered to not have long-term effects but can seriously impact compliance and adherence to a medication regimen.