Medications often interfere with allergy skin test interpretation. This study was performed to determine which medications interfere with allergy skin tests. We retrospectively reviewed skin-prick test results from patients who had discontinued H(1)-antagonists, tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), selective norepinephrine reuptake inhibitors (SNRIs), benzodiazepines, atypical antidepressants, antipsychotics, hypnotics, sedatives, proton pump inhibitors (PPIs), and H(2)-antagonists between 0 and 7 days before allergy skin testing. Ninety-seven subjects had taken second-generation H(1)-antihistamines within 7 days of skin testing; all patients who had stopped 3 days before testing had positive histamine controls. Two hundred sixty-eight skin tests performed on patients taking a single medication of interest showed that patients had the following percentages of a positive histamine control: TCAs, 56.5%; SNRIs, 100%; H(2)-blockers, 100%; SSRIs, 97%; PPIs, 97%; benzodiazepines, 85.7%; and atypical antidepressants/sedatives, 92.6%. The 580 patients taking multiple medications of interest showed that the odds ratio and 95% confidence intervals of a negative histamine test for patients taking TCAs were 6.33 (2.11-20.5), for H(1)-blockers were 4.95 (1.78-15.1), for benzodiazepines were 5.01 (1.72-15.80), for atypical antidepressants/sedatives were 3.11 (1.09-9.61), and for H(2)-blockers were 2.91 (0.97-9.37). The odds of a negative histamine test for SSRIs, SNRIs, or PPIs were not significantly increased. SSRIs, SNRIs, and PPIs are unlikely to interfere with skin testing. TCAs, H(1)-blockers, benzodiazepines, quetiapine, and mirtazapine should be discontinued temporarily if clinically able. H(2)-antagonists, bupropion, eszopiclone, trazodone, or zolpidem showed minimal interference with immediate hypersensitivity skin test histamine response.