How do some medication cause a person to gain (unwanted) weight?

Question

I have a friend who has gained 100 pounds when she went on a particular medication. (I suspect an anti-depressent.)

Does the med increase appetite?

Or what?

Answer 1

Some anti depressants do, personally I am on prednisolone which isn't an anti depressant it's like a drug to help my lungs because I have alot of lung issues and one of the side affects of that is gaining weight because it affects your eating and you tend to eat more, it's never affected me before but this time it has - when I say affect I mean after I eat dinner I'm super full then 10 minutes later I feel like I haven't eaten anything. To stop this I've just started drinking more water and eating fruits and veges, I pile my plate with vegetables so that if I do over eat there good things to eat, but in saying that I have gained weight, just some medications do affect people different ways.

Answer 2

due to 'water retention' by changing kidney behavior

or appetite change

or behavior change (less exercise)

or it can change 'basic metabolic rate'  (google it)

or a combination of the aboves

Answer 3

One possible mechanism to explain the weight gain is an enzyme that stimulates one's appetite. Anti-psychotic drugs increase the enzyme's activity four-fold.

But an increase of 100 pounds is almost out of the realm of possible weight gain due to an anti-psychotic. Average gains are typically below 30 (though this number varies depending on whose study you cite). Anything above that is probably rooted much deeper and not solely attributable to the drug. I would say 100 pounds indicates a very serious problem with motivation, moderation, and activity levels.

That gain could also be from a steroidal medication. They are well-known for increasing bulk.

Answer 4

So I am an MD/PhD psychiatrist and I mainly study weight gain in psychiatric patients and I can tell you there is no simple answer. Antidepressants (especially mirtazapine) can cause weight gain typically in the 5-20 pound weight range, I don't think I have ever heard of 100 pounds. Antipsychotics can definately cause >100 pounds in weight gain especially if started in children.

The mechanism of weight gain is controversial, but there are two leading hypothesizes. First is that many psychiatric drugs block histamine signaling in your brain. Histamine in the hypothalamus (the part of the brain that control appetite) is known to suppress feeding. Secondly, some drug likely act by blocking the serotonin 2C receptor, also in the hypothalamus of the brain.

Exactly, how this translates to increased weight gain is also unclear. Some people report clear increase in motivation to obtain food (being hungry all the time, getting up in the middle of the night to eat). Other people don't report increased desire to eat but instead say that they no longer can sense when they are full (decreased satiety).

100 pounds is definately a concern and would warrant a full medical work-up. There are a lot of conditions that can cause both depression and weight gain (such as hypothyroidism, sleep apnea, and Cushing's Disease). Your friend should be thoroughly evaluated and if it is still thought to be medication induced then there are a number of good psych meds that are not associated with weight gain.

Good Luck!