药物成瘾(drug addiction)，亦作药物依赖性（chemical dependency）。
服用某种对神经系统有特殊作用的药物（如麻醉剂、酒精或尼古丁）後，在躯体上和（或）精神上对其产生的依赖，患者虽然明知会造成伤害，但还是继续使用。躯体依赖性是由於反覆摄入，使机体对该种物质的耐受性和吸收能力愈来愈高，因此患者必须增加服用剂量，方能达到他所期望的效果。如果不增加服用剂量，就会产生戒断症状。精神性依赖可能与人的心理性格有较多的关系，有些人可能有遗传倾向容易成瘾。最常见的成瘾性药物是酒精、巴比妥酸盐、安定剂和苯异丙胺，还有会引起兴奋的尼古丁和咖啡因。初期治疗必须在医院的严格监督下进行。个人和团体的心理治疗也可发挥重要作用。支援团体，如嗜酒者互戒协会，在治疗酗酒方面已取得很大成功。实际上，能够承认自己服用毒品并决心改正，这是保证任何一种解毒治疗得以成功的最重要前提。
English version：
drug addiction
Physical and/or psychological dependency on a psychoactive (mind-altering) substance (e.g., alcohol, narcotics, nicotine), defined as continued use despite knowing that the substance causes harm. Physical dependency results when the body builds up a tolerance to a drug, needing increasing doses to achieve the desired effects and to prevent withdrawal symptoms. Psychological dependency may have more to do with one's psychological makeup; some people may have a genetic tendency to addiction. The most common addictions are to alcohol (see alcoholism), barbiturates, tranquilizers, and amphetamines, as well as to the stimulants nicotine and caffeine. Initial treatment (detoxification) should be conducted with medical supervision. Individual and group psychotherapy are critical elements. Alcoholics Anonymous and similar support groups can increase the success rate of other efforts. The ability to admit addiction and the will to change are necessary first steps.