What is the frequency of increased appetite as a side effect of mirtazapine (Remeron) use?

Increased Appetite with Mirtazapine: Frequency and Management

Increased appetite is a very common side effect of mirtazapine, occurring in approximately 11% of patients compared to 2% in placebo groups, with weight gain of ≥7% body weight reported in 7.5% of patients taking mirtazapine. 1

Prevalence of Increased Appetite

Mirtazapine has a well-documented effect on appetite stimulation:

• The FDA drug label specifically lists increased appetite as a common side effect, occurring in 11% of patients taking mirtazapine versus only 2% of those on placebo 1
• Weight gain of ≥7% of body weight was reported in 7.5% of patients treated with mirtazapine, compared to 0% for placebo 1
• In clinical trials, 8% of patients discontinued mirtazapine due to weight gain 1
• In pediatric trials (though not approved for this population), 49% of mirtazapine-treated patients had weight gain of at least 7% 1

Mechanism of Appetite Stimulation

Mirtazapine's appetite-stimulating effects are directly related to its pharmacological profile:

• Mirtazapine blocks central α2-adrenergic receptors and has high affinity for serotonin 5-HT2 and 5-HT3 receptors 2
• The blockade of 5-HT2 and 5-HT3 receptors is believed to contribute to its appetite-enhancing effects 2
• This unique mechanism distinguishes it from other antidepressants and explains why it's sometimes used specifically for patients with depression who also have poor appetite 3

Clinical Applications

Mirtazapine's appetite-stimulating effects have been utilized in specific clinical scenarios:

• In cancer cachexia management, mirtazapine has been recognized as an appetite enhancer, though further research is needed 4
• For patients with Alzheimer's disease experiencing weight loss, a retrospective study showed that 77.3% of patients gained weight after 3 months of mirtazapine treatment (mean gain of 1.93 kg or 3.9% of initial body weight) 5
• In inpatient settings, mirtazapine has shown numerical improvements in meal intake, though not significantly different from other appetite stimulants like dronabinol or megestrol 6

Timing and Onset of Appetite Effects

• Appetite stimulation typically begins early in treatment
• Effects on sleep and appetite may be noticeable within the first week of treatment 7
• Weight gain tends to continue with ongoing treatment, with studies showing continued gains at 3 and 6 months 5

Considerations and Cautions

When prescribing mirtazapine, be aware of:

• The FDA warns that mirtazapine should be used with caution in patients where weight gain might be problematic 1
• Mirtazapine is listed as a weight-gain-promoting medication in obesity management guidelines 4
• While useful for patients with both depression and poor appetite, mirtazapine should not be used solely for appetite stimulation without depression 3
• Monitor patients for excessive weight gain, which may become problematic for some individuals 3

Clinical Decision-Making Algorithm

1. For patients with depression and poor appetite/weight loss:

   • Mirtazapine may be an excellent first-line choice
   • Start with 15 mg at bedtime and titrate as needed for depression
   • Monitor weight regularly

2. For patients with depression without appetite concerns:

   • Consider alternative antidepressants if weight gain is undesirable
   • If using mirtazapine, counsel about potential appetite increase

3. For patients without depression seeking appetite stimulation:

   • Mirtazapine is not recommended solely for this purpose 3
   • Consider addressing underlying causes of poor appetite
   • Explore non-pharmacological approaches first

In summary, increased appetite is one of the most common and predictable side effects of mirtazapine, occurring in approximately 11% of patients, with significant weight gain in 7.5%. This effect can be beneficial in specific clinical scenarios but requires appropriate monitoring and patient counseling.