Background Antidepressants are established first-line treatments for anxiety disorders, but it is not clear whether they are equally effective across the severity range. Aims To examine the influence of baseline severity of anxiety on antidepressant efficacy for generalised anxiety disorder (GAD), social anxiety disorder (SAD), obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD) and panic disorder. Method Fifty-six trials of second-generation antidepressants for the short-term treatment of an anxiety disorder were included. Baseline and change scores were extracted for placebo and treatment groups in each trial. Mixed effects meta-regression was used to investigate the effects of treatment group, baseline severity and their interaction. Results Increased baseline severity did not predict greater improvement in drug groups compared with placebo groups. Standardised regression coefficients of the interaction term between baseline severity and treatment group were 0.04 (95% CI 70.13 to 0.20, P = 0.65) for GAD, 70.06 (95% CI 70.20 to 0.09, P = 0.43) for SAD, 0.04 (95% CI 70.07 to 0.16, P = 0.46) for OCD, 0.16 (95% CI 70.22 to 0.53, P = 0.37) for PTSD and 0.002 (95% CI 70.10 to 0.10, P = 0.96) for panic disorder. For OCD, baseline severity did predict improvement in both placebo and drug groups equally (b = 0.11, 95% CI 0.05 to 0.17, P = 0.001). Conclusions No relationship between baseline severity and drug-placebo difference was found for anxiety disorders. These results suggest that if the efficacy of antidepressants is considered clinically relevant, they may be prescribed to patients with anxiety regardless of symptom severity.