As previously discussed, mirtazapine can be more sedating at lower doses. Mirtazapine has a high affinity for the H₁ (histamine) receptor. This histamine blockade is thought to increase appetite and sedation. Weight gain with mirtazapine can be advantageous or a negative for some patients. One may ask, does weight gain follow a similar dose-dependent effect?

Unfortunately, mirtazapine works in many mechanisms and weight gain associated with its use is thought to be due to more than its antihistaminergic effects. It is thought that mirtazapine causes an activation of the TNF- cytokine system. One study conducted in Germany found a significant increase in weight gain, plasma TNF concentrations, and serum leptin levels. This is also seen in prior studies of patients taking clozapine. In general, plasma TNF-levels and circulating soluble TNF receptors are found to be positively correlated with body weight and can be seen in significantly higher levels in obese individuals.

Leptin levels appear to have a different relationship with bodyweight in humans than in animals. Animals with leptin deficiency are often found to be severely obese. However, in obese individuals, leptin levels are often increased and there is thought to be leptin resistance. When compared to venlafaxine, mirtazapine led to more weight gain and increased plasma concentrations of TNF and leptin. Venlafaxine did not cause a significant increase in weight, and some patients lost weight. Plasma levels of TNF and leptin remained unchanged in patients receiving venlafaxine.

While more research needs to be done to determine the exact trigger of the TNF-cytokine system activation in patients being treated with mirtazapine, it is unlikely that weight gain associated with mirtazapine is an adverse effect that is dose-dependent or will go away over time with continued use.

Did you enjoy this blog post? Subscribers are emailed new blog posts TWICE per week! In addition, you’ll get access to the free giveaways below. Over 6,000 healthcare professionals have subscribed for our FREE Giveaways. Why haven’t you?!

• 30 medication mistakes PDF
• 18+ Page Drug Interaction PDF
• 10 Commandments of Polypharmacy Webinar based on my experiences in clinical practice

Article written by Taylor Gill in collaboration with Eric Christianson, PharmD

Study Materials and Resources For Healthcare Professionals and Students – Amazon Books

References:

Anttila SA, Leinonen EV. A review of the pharmacological and clinical profile of mirtazapine. CNS Drug Rev. 2001;7(3):249-264.

Grasmäder K, Verwohlt PL, Kühn KU, et al. Relationship between mirtazapine dose, plasma concentration, response, and side effects in clinical practice. Pharmacopsychiatry. 2005;38(3):113-117.

Kraus T, Haack M, Schuld A, Hinze-Selch D, Koethe D, Pollmächer T. Body weight, the tumor necrosis factor system, and leptin production during treatment with mirtazapine or venlafaxine. Pharmacopsychiatry. 2002;35(6):220-225.

Stimmel GL, Dopheide JA, Stahl SM. Mirtazapine: an antidepressant with noradrenergic and specific serotonergic effects. Pharmacotherapy. 1997;17(1):10-21.