Eli5: why is there no test for the “chemical imbalance” that is often mentioned for depression?

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Eli5: why is there no test for the “chemical imbalance” that is often mentioned for depression?

In: Chemistry

33 Answers

Anonymous 0 Comments

Where exactly are you getting your facts from? People used to think diseases and viruses were a chemical imbalance, that’s how bloodletting became a thing..

Anonymous 0 Comments

“Chemical imbalance” is a pretty inexact way of describing the theories for how depression is driven by body chemistry. But in any case, that chemistry is largely in the brain. The brain is separated pretty strongly from the rest of the body (only a few chemicals can move into or out of the brain into the bloodstream) meaning that it’s not something that shows up on a blood test.

It’s also not as simple as the amount of single chemicals: the brain depends on a mix of different chemicals, whose behavior depends on the concentrations of the others and whose effects depend not just on the chemicals present but on the receptors available on each cell.

Anonymous 0 Comments

If it’s any similar to some other hormones like the HPA axis, it’s because there’s only a very low amount of that chemical circulating in your body at a time. Most of it is produced in your brain and used a very short distance ‘downstream’ from there, which effectively leads to undetectable amounts in the wider circulation. So if you took a blood sample from someone’s arm like we normally do, you would hardly detect the chemical, let alone be able to tell if there’s an imbalance. You’d have to take a blood sample inside the brain between the two specific points where the chemical is produced and absorbed again, to be able to tell anything at all.

That being said, things like depression or adhd are usually caused by neurotransmitter problems. They are molecules that you find in the brain and that allow one neurone to communicate with the next, but they are not found in blood much at all. So again you’d have to somehow sample the connection between two neurones to measure the amount of neurotransmitter.

An easier way to do it is to monitor the effect of drugs that affect neurotransmitters. If you give them SSRIs (serotonin reuptake inhibitors), what you are doing is forcing serotonin to be present for a longer time before it is reabsorbed, thereby making sure the signal travels correctly from one neurone to the next. Normal people will react differently to the drug compared to depressed people with a serotonin deficiency as it were. Compare it to to adhd meds: normal people on adderall act all high, while people with adhd on adderall are able to calm down

Anonymous 0 Comments

There are several parts to an answer:

1) As somebody already mentioned. (Major) Depression is actually “the symptom”. The underlying factors causing depression are varied and cannot be reduced to a single marker, as for example with diabetes. In short, the physiological mechanisms of depression (what is malfunctioning in the brain) are not fully understood and there is a lot of active research going on.

2) The chemical imbalance that you mention refers to neurotransmitters in specific parts of the brain, meaning, you would have to test the levels of such neurotransmitter directly in those areas, since a blood test would not be enough for that. And as I mentioned, even if you test this, this would only work for a very narrow group of patients, since the physiological causes of depression are very varied.

3) Not part of the answer, but if you google “depression biomarkers” you’ll find recent research regarding the kind of tests that could allow this. Which would be helpful for, for example, knowing what kind of depression the patient has.

TLDR It is possible to test this, but its a bit more complex than a blood test

Sources:
(1) I did neuroscience research for many years, including depression

(2) https://www.sciencedirect.com/science/article/abs/pii/S0166432817318521

Anonymous 0 Comments

Neuroscientist here: Because the “chemical imbalance” theory is bullshit. It was a real theory several decades ago, which was abandoned in the field because it doesn’t make sense / doesn’t work. But it is simple and easy to explain (despite being false) and therefore continues to propagate.

To be clear, it’s not that it’s a simplification. It’s just wrong.

If it WERE a chemical imbalance, it would be something you coughs test for, you are right about that, although the test would probably not be a blood test, might require a spinal tap or PET scan (best ways to measure specific chemicals in brain). It would also be simple to treat.

Pretty much ANY neat, simple story that someone tells you about the brain is usually false.

Anonymous 0 Comments

Because it’s bs. 99% of treated depression is not for medical reasons, it’s because the world is shit, or specifically that person’s life is more shitty than normal.

I wouldn’t explain it like this to a five year old though.

Anonymous 0 Comments

It’s because the chemical balance hypothesis was something that was devised by pharmaceutical companies as a marketing ploy, and has never been substantiated by any empirical evidence.

https://www.theguardian.com/society/2018/jan/07/is-everything-you-think-you-know-about-depression-wrong-johann-hari-lost-connections

Even psychiatry is admitting to this, these days: https://www.psychiatrictimes.com/view/debunking-two-chemical-imbalance-myths-again

Anonymous 0 Comments

You’d probably need a pre- disorder reading of a test to be able to compare changes from their baseline but most depressed people don’t go to the doctor months before they feel unwell to get a baseline test just in case.

Anonymous 0 Comments

“Chemical imbalance” is an unproven theory that is embraced because it sounds nice. Much better to say, “I’m depressed because of a chemical imbalance in my brain” than, “I’m depressed because I’ve made a mess of my life.”

If we want people to seek treatment, we have to remove the shame.

Anonymous 0 Comments

So usually tests are done in blood since that’s easily accessible. The chemical imbalance that occurs in mental illness is a chemical imbalance of neurotransmitters. Basically those chemicals aren’t available in your blood, but inside your brain, and even in “normal” brains, they get reabsorbed or degraded fairly fast, so you couldn’t even really measure it in cerebrospinal fluid, since the chemicals wouldn’t be widely available there. Only way to test it would maybe doing a biopsy of a fairly large chunk of the brain and test the presence or absence of said chemicals, but for obvious reasons, that wouldn’t be a procedure that’d be useful at all. There are some tests that have been used before to sorta look at the somatic, biological side of the equation. MRI can be used to measure blood flow to certain areas of the brain, and if some areas are less or more active than others you can sorta deduce it’s degree of chemical activity, but this type of test isn’t done usually because a) it’s super expensive b) even though treating depression is hard, diagnosing it is fairly easy, and can be done in just a couple of sessions of talking to your patient, and c) said changes usually occur in very subtle ways, in quite severe depression, so at that point it has little diagnostic use. It has been used in research though, but fairly useless in clinical practice