Drug treatment of panic disorder. Comparative efficacy of alprazolam, imipramine, and placebo. Cross-National Collaborative Panic Study, Second Phase Investigators.

The Cross-National Collaborative Panic Study, Phase Two, compared alprazolam with imipramine and with placebo in a sample of 1168 randomly assigned subjects. The study, conducted at 12 centres, assessed clinical change over eight weeks of double-blind drug treatment. Improvement occurred with alprazolam by week 1 and 2, and with imipramine by week 4. By the end of week 8, however, the effects of the two active drugs were similar to each other, and both were superior to placebo for most outcome measures.