Mirtazapine is a very strong H1 receptor inverse agonist and, as a result, it can cause powerful sedative and hypnotic effects.[1] A single 15 mg dose of mirtazapine to healthy volunteers has been found to result in over 80% occupancy of the H1 receptor and to induce intense sleepiness.[81] After a short period of chronic treatment, however, the H1 receptor tends to desensitize and the antihistamine effects become more tolerable. Many patients may also dose at night to avoid the effects, and this appears to be an effective strategy for combating them.