Effects of the brain-penetrant and selective 5-HT6 receptor antagonist SB-399885 in animal models of anxiety and depression. Do not start, stop, or change the dosage of any medicine before checking with them first. Combining this with tiessaistes mirtazapine medication has been shown to be more effective than drugs alone. What other drugs will affect mirtazapine? Cold or allergy medicine, narcotic pain medicine, sleeping pills, muscle relaxers, and medicine for seizures, depression or anxiety can add to sleepiness caused by mirtazapine. If getting up slowly doesn help, or if this problem continues, notify your doctor. Only people who dont get up off their dead ends dont take advantage of these services. Mirtazapine has an elimination half-life of approximately 20 to 40 therefore, dose changes should not be made at intervals of less than one to two weeks in order to allow sufficient time for evaluation of the therapeutic response to given dose.