Mirtazapine, is a moderate antagonist at muscarinic receptors, a property that may explain the relatively low incidence of anticholinergic side effects associated with its use. Pharmacokinetics Mirtazapine Tablets, USP are rapidly and completely absorbed following oral administration and have a half-life of about 20 to 40 hours. SIDE EFFECTS Associated With Discontinuation Of Treatment. Approximately 16% of the 453 patients who received REMERON (mirtazapine) Tablets in US 6-week controlled clinical trials discontinued treatment due to an adverse experience, compared to 7% of the 361 placebo-treated patients in those studies. SIDE EFFECTS Associated With Discontinuation Of Treatment. Approximately 16% of the 453 patients who received REMERON (mirtazapine) Tablets in US 6-week controlled clinical trials discontinued treatment due to an adverse experience, compared to 7% of the 361 placebo-treated patients in those studies. It may be the preferred antidepressant in anorexic elderly individuals with insomnia. 21 The most common side effects of mirtazapine are dose-dependent drowsiness (54%), dry mouth (25%), increased appetite (17%), weight gain (12%), and dizziness (7%). 10 These side effects tend to diminish with time. Further systematic study is needed to evaluate the use of mirtazapine in the treatment of. Side Effects. Drug information provided by: IBM Micromedex. Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Side Effects. See also the Warning section. Dizziness, drowsiness, lightheadedness, increased appetite, weight gain, dry mouth, or constipation may occur. The side effects featured here are based on those most frequently appearing in user posts on the Internet. The manufacturer's product labeling should always be consulted for a list of side effects most frequently appearing in patients during clinical studies. Talk to your doctor about which medications may be most appropriate for you. Side Effects. See also the Warning section. Dizziness, drowsiness, lightheadedness, increased appetite, weight gain, dry mouth, or constipation may occur. Indications, dose, contra-indications, side-effects, interactions, cautions, warnings and other safety information for MIRTAZAPINE. Along with its needed effects, mirtazapine (the active ingredient contained in Remeron) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.