eli5 How do antidepressants and other medications cause someone to *gain* weight?
In: 90
I’ve asked this question to several of my prescribing doctors and they say the answer isn’t clearly known. Some meds increase appetite and some meds even if you’re extremely careful about what you eat, counting calories & eating only healthy whole nutrition, still cause weight gain.
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The exact causes of weight gain [from antidepressants] is scientifically blurry: no one has a clear answer. I have encountered this weight in my own clinical recovery from depression.
When you start antidepressants, in most cases, the prescriber wants you to put that weight on. The reason is that, by the time the average person goes to their doctor about depression, they may have experienced many months of poor diet and nutrition: a common symptom in depression.
So if you get an increased appetite, or your body starts stockpiling, (no one knows) they’re okay with it. After a couple of years, the weight disappears – again, no one knows why.
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There are several explanation. From my expiriance, mostly by increase in water retention or increase in appetite. There might be some other explanations (insulin, hunger hormones, sex hormones etc.)
Also, some of my patients gain weight on antiallergens (antihistamines). My guess is that it makes them less active due to known effects on sleep cycle and general feeling of tiredness.
All in all, no medication can really make someone gain weight, only food can (Laws of thermodynamics). But it might affect hunger, water consumption/retention, energy expenditure or physical activity.
This is a bit of a loaded question as most common antidepressants aren’t actually associated with significant weight gain on average. Mirtazapine, paroxetine, and older tricyclic antidepressants like amitriptyline are exceptions.
Anyway, medications with the most weight gain frequently block receptors involved in appetite regulation, including certain histamine and serotonin receptors. Some drugs don’t increase fat gain but increase water/salt retention. Steroids like prednisone have a huge range of effects on how cells function and can cause shifts in where fat is stored along with weight gain. Appetite is really complicated and there are parts we don’t understand, but certain drug actions predictably increase weight and/or appetite.
According to one of my doctors, amitriptyline increases the body’s ability to absorb nutrients. It doesn’t discriminate, it just increases absorption.
A very similar medication, protriptyline, does not have this side effect.
Source: I was prescribed the med to increase absorption due to a medical condition. I know others who have been prescribed it due to a limited ability to absorb fat.
In my experience, it’s extremely rare a doctor knows this is what’s happening. When I explain even to other GI doctors that’s why I take/took the drug, they don’t believe me until reading the notes from my prior GI.
No idea about why other antidepressants have that side effect.
TLDR : they block the uptake of Leptin in the brain, the chemical that tells you that you are full. You keep eating = weight gain.
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