DH - There are no dumb questions when it comes to putting drugs into body. As CQ said, all of the antidepressants have a different propensity to cause weight gain, some more than others. The older tricyclic antidepressants (TCAs - eg. Elavil™ [amitriptyline], Tofranil™ [imipramine]) and especially the monoamine oxidase inhibitors (MAOIs - eg. Nardil™ [phenelzine], Parnate™ [tranylcypromine]), because they block muscarinic receptors and histamine receptors, all seem to cause significant weight gain in most (but not all) people.

The different selective serotonin reuptake inhibitors (SSRIs) can cause weight gain to varying degrees. Paxil™ (paroxetine) seems to be the worst offender, although it is probably the best SSRI for relieving anxiety. Next in line (again, for many people) is probably Zoloft™ (sertraline). After that, the lines begin to blur: maybe Luvox™ (fluvoamine) is next, followed by Celexa™ (citalopram), Lexapro™ (escitalopram), and Prozac™ (fluoxetine). It is presently impossible to determine ahead of time if you will gain weight while taking an SSRI, but unfortunately it does seem that the better the drug relieves depression, the more pronounced the weight gain.

The SSRI weight gain may be due to the altering the concentration &/or activity of a certain subset of serotonin receptors (5HT-3). Paxil may cause more weight gain than the others because it blocks muscarinic receptors, as well, which is well documented as a mechanism of weight gain with many psychiatric medications. Other mechanisms of weight gain have been proposed (altering of electrical activity in the hypothalamus or other structures in that area of the brain). Another proposed mechanism of weight gain is is that a symptom of depression is decreased appetite and weight loss. As one recovers from the depressive episode (ie. the depression goes into remission) the appetite is recovered and one gains weight. In other words, we aren't certain why weight gain occurs.

The weight gain with the SSRIs is very incidious seems to be a delayed reaction. With most people, the weight gain seems to appear from nowhere. Eight to twelve weeks into therapy one's clothes suddenly don't fit. If a person's lifestyle is closed gone over, it can be seen that a carbohydrate craving builds and more junk food (chips and cookies) seem to find their way into the person's diet. I cannot stress enough that not everyone gains weight when taking antidepressants. I have found that approximately 60% - 70% of people taking SSRIs do gain weight (this is my estimate, from my clinical experience, and is not only my impression, not scientifically determined).

Now the good news/bad news part: the good news: one can avoid the weight gain if (and this is a very big IF) one watches their diet very closely and follows an individually-tailored (healthy) exercise program. Keeping a food diary of everything you eat does help quite a bit, as it is an at a glance look at how much we eat. It especially shows those little munchy-type things we eat without really thinking about it. It does seem that the weight gain does level off after being on the SSRI for 9 months to a year. The bad news is is that the weight gain caused by SSRIs may well be irreversible; once the weight is gained it is near impossible to lose. Now, in saying this, again there are exceptions to this "rule". I have seen people lose weight while taking SSRIs. It is a matter of playing the numbers game when it comes to side effects, and we can only deal in generalities.

As for Remeron™ (mirtazapine), I have had less clinical experience. What I do know is that, in regards to weight gain, it probably, no, it does, cause more weight gain, more quickly than the SSRIs. Sedation can also be a problem (unless one is having problems with sleep disturbances).

Effexor™ (venlafaxine) does not seem to be as much of a problem as the SSRIs in the area of weight gain. It is more likely to be weight neutral in the area of weight gain; although I have seen people gain weight with this drug (but not as often as with the SSRIs).

The antidepressant with the least amount of weight gain is Wellbutrin™ (bupropion). This drug does not directly affect serotonin receptors, and it's mechanism is unknown (the proposed mechanism of modulating norepinephrine and blocking dopamine reuptake does not seem plausible to me). For awhile there was a lot of talk about Wellbutrin causing weight loss; more recently tthe drug is considered to be weight neutral. One can gain weight while taking Wellbutrin, although it is not as much of a shock as is seen with the SSRIs.

Well, I think I've blathered on long enough. If you have any specific questions, I'll be glad to help. - Cam

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