Why do some anti depressants make you gain weight?

Pharmacist here

The fact of the matter is - no one understands exactly why some antidepressants cause weight gain and others do not. The brain is pretty much a soup of chemicals and each separate chemical performs a huge variety of different actions dependent on what molecule it is interacting with on a neuron. We know antidepressants work by affecting levels of neurotransmitters, like dopamine, serotonin, and norepinephrine, and know how some of these neurotransmitters work in several instances. However, how those neurotranmistters work in every single cell of the body is not understood, so slightly affected the levels of one versus another can have wide and varying affects throughout your entire body's chemistry.

Just as a for instance with the widely varying chemical effects in the body - in the kidneys there is an enzyme called angiotensin-converting enzyme. A class of drugs blocks this chemical from working, and through a complex pathway works to lower your blood pressure. However, this same enzyme ALSO exists in your lungs, but there it's called bradykininase. When you take one of these medications, some people start coughing for no reason because the drug is blocking this same chemical from doing its job in two completely different parts of the body.

Much of this can be paralleled with the neurotransmitters that affect your depression, but there is so much that we just do not understand with how they affect all of the systems of the body. Serotonin for example also acts as a regulator of your bowels. For the time being, unfortunately, the answer to your question is globally, "We don't know!"

Just going on personal experience from 10 years of on/off/on various anti-depressants (Paxil, Zoloft, Lexapro, Wellbutrin)...everyone has a different reaction to different drugs. If the weight gain bothers you that much, use objective measurements to help you out. How much are you eating? How much are you sleeping? How hard/often are you exercising? And the worst part is that you may have to compensate additionally to counter the drugs.

I will say that before I started Paxil, I was probably in the best shape of my life...20 lbs lighter than I am now. I worked out religiously. Almost neurotically...2 hrs/day for 5 days/week. When I started Paxil, I soon didn't care about working out. Ironically, I was more at peace with myself and happier with myself, and didn't care if I wasn't in great shape. I enjoyed life, enjoyed food, and eventually it took a lot more alcohol to gain wait. When I was working out, I was getting the endorphin rush from it, which was motivation to keep working out. On the drugs, that lull from not working out wasn't there...so I didn't work out nearly as much.

Eventually, i went off the drugs. Nothing really happened weight-wise, until I started caring about the weight. I think it was at least a year or two after stopping that I decided to start running. The endorphin rush kicked in, the running became addictive, and the weight fell off. About a year ago, started up on Zoloft. Urge to workout decreased, weight came back. I never really noticed a change in my appetite volume-wise, but I did notice that I cared less about eating quality foods. The Zoloft has also affected my sleep patterns, which I'm betting will also impact metabolism.

I'm sure age and lifestyle has contributed as well, but there has been a direct effect from the drugs. My advice is to regulate your behavior and enlist a loved one to help be an impartial observer. It may be harder to lose weight, but it's not impossible.

Okay hopefully I can make this not too medical for you but SSRI is a class of drug used to treat depression, anxiety, and other mood type disorders. A drug class is just pretty much what the drug does like anti-hypertensive drug but because you don't know what SSRI's really are if you aren't in the medical field it seems like a type of drugs. Because there are many drugs in this class of drugs, they all have there own side effects good vs bad. Hopefully you understand the point I am trying to get across.

Hello, I have a medical degree and have taught psychiatry, neuroscience and pharmacology at Cambridge and Manchester Universities, although I quit being a clinician and a lecturer to set up a business. I also have taken quite a few different antidepressants in my time.

For what seems like a very simple question there is quite a complex answer. I will try and explain it with as little medical jargon as possible.

1. No-one knows exactly why. It is likely there are many mechanisms involved, but researchers have worked out some of those.

2. If you give 100 people Prozac (as an example). some will gain weight and others will lose it. One drug does not necessarily have the same effect on everyone as we all have different genetics. Genetics can alter the way a drug is processed by the body and the molecular consequences on a cerebral neuron (brain cell).

3. Depression causes reduced appetite and so consequently when people recover many gain the weight back again.

4. Although SSRI is supposed to stand for selective serotonin re uptake inhibitors the reality is they are not 100% selective. They also have an effect on other receptors that are present in the brain. For example:



Secondary binding properties of SSRIs

Citalopram (Celexa) most selective serotonin reuptake inhibitor

Escitalopram (Lexapro) most selective serotonin reuptake inhibitor


Fluoxetine (Prozac) least selective serotonin reuptake inhibitor
norepinephrine reuptake
dopamine reuptake
serotonin-2C receptors
cytochrome P450 2D6
cytochrome P450 3A4


Paroxetine (Paxil) muscarinic cholinergic receptors (most potent blocker of muscarinic receptors among the SSRIs)
histamine H1 receptors
nitric oxide synthase
cytochrome P450 2D6


Sertraline (Zoloft) dopamine reuptake (more potent dopamine uptake inhibitor than other SSRIs)
norepinephrine reuptake
sigma receptors

As the above demonstrates, some ADs also block the histamine H1 receptor and the muscarinic receptor (Paxil is worst for this). Blocking both these receptors is a cause of weight gain, hence why Paxil is one of the worst culprits when it comes to piling on the pounds.


5. Another factor in SSRI weight changes is timing. On average when someone starts an SSRI they will lose weight for a few weeks and then start gaining. By the end of year one on average someone on SSRIs will be 5 lbs heavier. No-one understands why this is, but my personal guess is it is because the side effects of nausea are worst at the start to treatment as the body gets accustomed to taking the drug.


6. The last thing to remember is neuroscience and neuropharmacology are rapidly advancing areas of medical research (hence why I chose to be come a research scientist in these disciplines) . The truth is we probably know less than half of the reasons people react differently to psychopharmcological drugs, but in the coming years our understanding will increase rapidly.

They don't make you gain weight.

They can effect you in terms fo making you more tired and lowering how many calories you burn. Or make you more hungry and cause you to eat more.

If you track your activity, and calories... you'd be fine.

Agree, I'm a psych nurse and previous was on citalopram for five years. If you eat well, and exercise more, you shouldn't gain weight. This is the advice we give to our patients.

Neither my other half nor I have any first-hand experience with antidepressant drugs, but one of my favorite health books is The End of Diabetes by Joel Fuhrman, who on his website writes about natural treatments for depression, none of which promote weight gain.

http://www.drfuhrman.com/library/natural_depression.aspx

I have no strong feelings for or against medication. It's just that I am lazy and like it simple, so if my body's immune system can handle it, there's one less pill box to administer. Heck, I don't even get a flu shot, even though my doctor has been begging me for years.

@kristinanicol

as a fellow bipolar i have taken both seroquel and zypyrexa. both are dreadful for weight gain but my opinion from my experience is zypyrexa is the worst

when i was last in hospital they had no beds for acute mania so they put me on the eating disorders wing! I was shocked to see the nurses load up the anorexics on the zypyrexa TO MAKE THEM GAIN WEIGHT! That is just how bad these antipsychotics are

although the weight gain is bad i have never been as well as on my now combo of lamictal and seroquel and would not try any other med!

I cannot get over the sweet carb cravings... I try taking salads for lunch but by the time I get home, its insatiable... I'm on Wellbutrin XL... I was working out but since the depression started, I still only want to sleep. I will only go for walks a couple days a week but it's the cravings that are killing me... any advice for the cravings?! I was taking cereal with Silk milk to work every single day for the last couple of months but have now tried to eat salad for lunch but it's killing me...