Antidepressants And Weight Gain

Here are some of the causes of
antidepressant weight gain

There is a well-known association between antidepressants and weight gain. However, no-one really knows the mechanism behind weight gain and antidepressants. It seems that antidepressant weight gain is caused by a number of factors and in this article we intend to address some of the reasons why people put on weight when they use antidepressants.

Also, some of the theories that we cover are just that, theories, and may not have been verified by scientific research at this stage.

Antidepressants and weight gain, possible causes:

Decreased 'Sympathetic Tone'

Increased Insulin Resistance

Affects Hypothalamic Function

Decreased 'Sympathetic Tone'

'Sympathetic Tone' is a term used to describe the activity of the sympathetic nervous system (SNS). The SNS innervates various organs and systems in the body and by doing so increases calorie or energy expenditure of that organ or system.

Accordingly, someone with a naturally high 'sympathetic tone' generally has a fast metabolism and someone with a low 'sympathetic tone' has a slow metabolism.

Now, some antidepressants work by inhibiting the re-uptake of the neurotransmitters into the neurons from which they came. An example is Selective Serotonin Re-uptake Inhibitors (SSRIs). This means they remain in the synapse between the neurons and keep stimulating the targeted neurons. Of course, this occurs in all neurons throughout the body not just those neurons in the brain.

One theory states that, if these neurotransmitters keep stimulating the receptors on the targeted neurons, over time, the receptors become de-sensitised to the action of the neurotransmitters. This is a similar effect to how insulin resistance works.

If this theory is correct, over time, the 'sympathetic tone' would decrease because there is less stimulation of the targeted organs and systems of the body. This results in a slowing of the metabolism and a decrease in overall calorie expenditure, which may be contributing factor of antidepressants and weight gain despite an iso-caloric (the same number of calories) food intake.

Increased Insulin Resistance

There is a good body of research now indicating that certain antidepressants may result in insulin resistance, which may therefore be another cause of antidepressants and weight gain.

The mechanism through which this occurs has been largely unknown until a few years ago when researchers in Israel found that certain antidepressants affect enzymes involved in insulin signalling in cells, which may then induce insulin resistance.

Affects Hypothalamic Function

The association between weight gain and antidepressants may also result from the impact these drugs have on the levels of phospho-AMPK in the hypothalamus.

Hypothalamic AMPK is linked to the food regulating hormone, leptin, and when levels of AMPK rise leptin is inhibited. Since leptin has appetite-suppressing effects, when it is inhibited by AMPK we become ravenous and may eat enormous amounts of food. This of course, results in antidepressant weight gain.

For these reasons the association between antidepressants and weight gain is clear even though some of these theories are yet to be proven.

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