同时使用两种或两种以上药物时有可能产生相互作用。这种相互作用可能是有害的(见前文)。也可能是有益的,能增加疗效或减少毒性。此种有益的相互作用最突出的例子就是抗结核药的合并用药和抗高血压药的合并用药。例如,我们常见的治疗结核的药物为异烟肼,链霉素和对氨基水杨酸,这三者中任何二者的联合应用,不仅作用增强,还可延缓结核杆菌耐药性的产生。又如,抗高血压药联合应用时,有些药物可降低心脏输出量而另一些药物可降低外周血管的阻力,因而大大提高降压效 Interactions may occur when two or more medications are used at the same time. This interaction can be harmful (see above). It may also be beneficial to increase the efficacy or reduce the toxicity. The most prominent examples of such beneficial interactions are combinations of anti-TB drugs and anti-hypertensive drugs. For example, the combination of isoniazid, streptomycin, and p-aminosalicylic acid, our common drug for the treatment of tuberculosis, not only enhances but also delays the development of mycobacterial tuberculosis drug resistance. In another example, antihypertensives combined application, some drugs can reduce cardiac output and other drugs can reduce peripheral vascular resistance, thus greatly reducing blood pressure lowering effect