Drug tolerance or drug insensitivity is a pharmacological concept describing subjects reduced reaction to a drug following its repeated use. Increasing its dosage may re-amplify the drugs effects; however, this may accelerate tolerance, further reducing the drugs effects. Drug tolerance is indicative of drug use but is not necessarily associated with drug dependence or addiction. The process of tolerance development is reversible (e.g., through a drug holiday) and can involve both physiological factors and psychological factors.One may also develop drug tolerance to side effects, in which case tolerance is a desirable characteristic. A medical intervention that has an objective to increase tolerance (e.g., allergen immunotherapy, in which one is exposed to larger and larger amounts of allergen to decrease ones allergic reactions) is called drug desensitization.The opposite concept to drug tolerance is drug reverse tolerance (or drug sensitization), in which case the subjects reaction or effect will increase following its repeated use. The two notions are not incompatible and tolerance may sometimes lead to reverse tolerance. For example, heavy drinkers initially develop tolerance to alcohol (requiring them to drink larger amounts to achieve a similar effect) but excessive drinking can cause liver damage, which then puts them at risk of intoxication when drinking even very small amounts of alcohol.Drug tolerance should not be confused with drug tolerability, which refers to the degree to which overt adverse effects of a drug can be tolerated by a patient.
Sertraline, sold under the brand name Zoloft among others, is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. The efficacy of sertraline for depression is similar to that of other antidepressants, and the differences are mostly confined to side effects. Sertraline is better tolerated than the older tricyclic antidepressants, and it may work better than fluoxetine for some subtypes of depression. Sertraline is effective for panic disorder, social anxiety disorder, generalized anxiety disorder, and obsessive–compulsive disorder (OCD). However, for OCD, cognitive behavioral therapy, particularly in combination with sertraline, is a better treatment. Although approved for  post-traumatic stress disorder, sertraline leads to only modest improvement in this condition. Sertraline also alleviates the symptoms of premenstrual dysphoric disorder and can be used in sub-therapeutic doses or intermittently for its treatment.Sertraline shares the common side effects and contraindications of other SSRIs, with high rates of nausea, diarrhea, insomnia, and sexual side effects, but it appears not to lead to much weight gain, and its effects on cognitive performance are mild. Similar to other antidepressants, the use of sertraline for depression may be associated with a higher rate of suicidal thoughts and behavior in people under the age of 25. It should not be used together with MAO inhibitor medication: this combination causes serotonin syndrome. Sertraline taken during pregnancy is associated with a significant increase in congenital heart defects in newborns.Sertraline was invented and developed by scientists at Pfizer and approved for medical use in the United States in 1991.