Medical Conditions to Rule Out Before a Psychiatric Diagnosis

Before settling on a diagnosis of depression, anxiety or ADHD, a clinician should ask whether a medical problem, a medication or a substance could be causing or worsening the symptoms. The usual suspects are thyroid disease, anemia, vitamin B12 deficiency, sleep apnea, medication side effects, alcohol or other substances, and, for many women in midlife, perimenopause.

There is no single standard "psychiatric blood panel". The American Psychiatric Association's guideline says lab and other tests should be chosen based on how likely the result is to change the diagnosis or treatment, and warns that routine, untargeted testing brings costs and false positives that are unlikely to be worth it. The tests that make sense depend on your symptoms, history and risk factors.

Why medical causes matter

Many physical conditions produce exactly the symptoms that depression and anxiety questionnaires count: fatigue, poor sleep, low energy, slowed thinking, restlessness and trouble concentrating. The APA guideline gives examples: an overactive thyroid can cause anxiety, and someone with kidney failure (uremia) or obstructive sleep apnea may feel apathetic, fatigued and inattentive, wrongly suggesting depression even when mood has not changed. The PHQ-9's authors likewise expected clinicians to rule out physical causes of depression before diagnosing it.

Finding a medical contributor does not always mean the psychiatric condition is "not real". Often both are present and both need treatment. But missing a medical cause can mean months of medication trials for a problem that a thyroid pill, iron or a CPAP machine would address.

The conditions most worth checking

Thyroid disease

The American Thyroid Association lists feeling tired, feeling sad or down and forgetting things easily among the symptoms of an underactive thyroid, and notes that not everyone has all of them and that other health problems can cause them too. A blood test is the only way to know for sure, and TSH is one of the two main tests. An overactive thyroid points the other way, toward anxiety, irritability, difficulty sleeping and a racing heart. The U.S. Preventive Services Task Force found insufficient evidence to screen adults without symptoms, but that statement applies only to people with no symptoms; once you have symptoms, testing is a clinical decision. Thyroid, cortisol and ADHD covers how thyroid problems can also mimic attention difficulties.

Anemia and vitamin B12

Anemia can cause tiredness, weakness, dizziness and shortness of breath, all of which can be mistaken for the low energy of depression, and it is diagnosed with a complete blood count. Vitamin B12 deficiency deserves separate attention. England's 2024 NICE guideline says symptoms vary and are often not specific to B12, that deficiency can be associated with depression, anxiety or psychosis, and that it should not be ruled out just because there is no anemia. NICE advises testing people who have at least one common symptom and at least one common risk factor. Risk factors it lists include:

• A diet low in B12, such as a vegan diet, without regular supplements
• Use of metformin, proton pump inhibitors or H2-receptor antagonists (common acid-reflux drugs)
• Previous gastrointestinal surgery, including many bariatric operations
• Autoimmune conditions, including thyroid disease
• Recreational nitrous oxide use

More on the link between B12 and mood is in depression and vitamin B12 deficiency.

Sleep apnea

The National Heart, Lung, and Blood Institute lists daytime sleepiness and tiredness that can lead to problems with learning, focusing and reacting, along with insomnia, fatigue and headache, which it notes are more common in women. In children, sleep apnea can show up as overactivity and trouble paying attention in school. Loud snoring, breathing that stops and starts, and gasping at night are the clues to mention. Canadian ADHD guidelines specifically warn that sleep apnea and anemia can produce positive results on ADHD rating scales. If sleep is a big part of the picture, sleep study or insomnia treatment? helps you decide which you need.

Medications

The APA guideline recommends that every initial psychiatric evaluation review all prescribed and non-prescribed medicines, herbal and nutritional supplements and vitamins, and their side effects. Two well-documented examples:

• Corticosteroids such as prednisone. The prescribing information warns that psychiatric changes ranging from euphoria, insomnia and mood swings to severe depression and psychosis may appear, and that existing emotional instability may be aggravated.
• Montelukast (Singulair), an asthma and allergy medicine. In 2020 the FDA required a boxed warning about serious neuropsychiatric events, including agitation, depression, sleep problems and suicidal thoughts or actions, in people with and without a history of mental illness.

Do not stop a prescribed medicine on your own because you suspect it is affecting your mood. Tell the prescriber, who can weigh the risks and alternatives. The montelukast warning is an exception the FDA spells out: it advises patients to stop the drug and contact a health care professional right away if mood or behavior changes occur.

Alcohol and other substances

The APA guideline recommends asking every new patient about tobacco, alcohol, cannabis and other drugs, and about misuse of prescribed or over-the-counter medicines. The National Institute on Alcohol Abuse and Alcoholism notes that anxiety-like symptoms can follow even a single heavy drinking episode, that stopping drinking often leads to improvement in co-occurring mental health conditions, and that the key diagnostic tool is a timeline: are the symptoms present during periods without alcohol? Being candid about use is one of the most useful things you can do in an evaluation. Psychiatric medications and alcohol covers what mixing does.

Perimenopause

A joint guideline from The North American Menopause Society and the National Network of Depression Centers describes perimenopause as a window of vulnerability for depressive symptoms and major depressive episodes, notes that most women who have an episode in perimenopause have had one before, and says menopause symptoms such as hot flashes and sleep disturbance complicate and overlap with depression. It recommends that diagnosis include identifying menopausal stage, assessing both psychiatric and menopause symptoms, and considering other diagnoses. Treatment options are compared in perimenopause depression: hormone therapy, antidepressants or both.

Before an ADHD diagnosis

The same principle applies to attention problems. Canadian ADHD guidelines say a thorough history, functional review and physical examination may highlight underlying physical conditions, and that while most people with ADHD do not need laboratory tests as part of their diagnosis, in certain cases a lab work-up or specific tests, such as a sleep study, are needed to rule out a suspected problem. Poor sleep, anemia, thyroid disease and substance use are worth considering whenever concentration problems began recently or do not fit a lifelong pattern.

A worked example

A woman in her late forties tells her clinician she has felt flat, exhausted and foggy for six months, wakes at 3 a.m. most nights and has a PHQ-9 in the moderate range. A careful evaluation asks more questions before settling on major depression. Her periods have become irregular and she has night sweats, which raises perimenopause. Her partner says she snores and sometimes stops breathing, which raises sleep apnea. She has taken a proton pump inhibitor for acid reflux for years, a B12 risk factor, and has some memory complaints, a common B12 symptom. She drinks two or three glasses of wine most evenings to help her sleep, and alcohol can disturb sleep and mood in its own right.

None of these findings rules out depression. But together they shape the plan: a sleep study, a B12 test, a talk about alcohol, input from her gynecologist about menopause symptoms, and, if depression is confirmed, treatment that accounts for all of it. That is the difference between an evaluation that asks "how depressed are you?" and one that asks "why?"

When a medical cause is found

Treating the medical problem is the first step, but it is not always the last. Mood symptoms may improve fully, partly or not at all once the physical cause is treated, and depression or anxiety that has taken hold may still need its own care. Keep the psychiatric clinician informed of new diagnoses and treatments, because medical medicines and psychiatric medicines can interact, a point the APA guideline makes explicitly.

What is standard, and what is not validated

There is no universal list, but the pattern across the sources above is clear: tests are chosen to answer a question raised by your symptoms and history.

Genetic tests that claim to predict medication response sit in a gray zone of their own; pharmacogenomic testing: coverage, limits and when it helps explains what they can and cannot do.

What to bring and what to ask

• A list of every medication, supplement and vitamin, with doses and start dates, including recent courses of steroids or new prescriptions
• Recent lab results from your primary care doctor, so tests are not repeated unnecessarily
• Notes on sleep: snoring, waking up gasping, daytime sleepiness
• For women in midlife: changes in cycles, hot flashes or night sweats
• An honest account of alcohol, cannabis and other substance use
• Diet and surgical history relevant to B12 (vegan diet, bariatric surgery)

Questions worth asking your clinician:

• Which medical causes have been considered for my symptoms?
• Which tests do you recommend, and how would each result change the plan?
• Can you coordinate with my primary care doctor on results?
• If a test comes back abnormal, who will treat it?

Good communication between your psychiatrist and primary care clinician makes all of this easier; see how your psychiatrist and primary care doctor should work together.

When symptoms are urgent

Some changes need same-day medical attention rather than an outpatient appointment: sudden confusion, new severe headache, symptoms after a head injury, hallucinations appearing for the first time, or mood changes with high fever. If you are thinking about suicide or are in crisis, call or text 988 (the 988 Suicide & Crisis Lifeline) or go to the nearest emergency room.

How the practice approaches medical contributors

Dr. Lewis's 75-minute Health Strategy Session includes a review of health history and the option to discuss comprehensive bloodwork and functional medicine testing if appropriate. The practice's ongoing care includes lab testing alongside psychiatric evaluation, medication management and psychotherapy, and lab costs are separate from visit fees. Its DISCOVER program pairs an assessment with advanced bloodwork and functional labs; the program's own page says some of those tests (mycotoxin, toxic-metal and intestinal-barrier panels) are investigational and not validated for diagnosis, and that Dr. Lewis explains what each can and cannot tell you. Details are on the lab testing page and in DISCOVER assessment and labs: what to expect. For how evaluation fits with other kinds of assessment, see psychiatric evaluation vs psychological testing, and the Choosing Psychiatric Care guide for the wider picture.

Frequently asked questions

Should everyone with depression get their thyroid checked?

Not automatically. Testing is most useful when symptoms or history suggest a thyroid problem, such as fatigue with feeling cold, weight change, or a family history. Ask your clinician whether it makes sense for you, and bring any recent results.

My labs were normal. Does that mean my symptoms are psychiatric?

Normal results make the tested causes less likely, but labs cover only some possibilities. Sleep problems, medications, substances and life stressors also matter, and psychiatric and medical conditions often coexist.

Can a vitamin deficiency cause anxiety?

Vitamin B12 deficiency can be associated with anxiety, depression or psychosis according to NICE. Whether a test is worthwhile depends on whether you also have risk factors such as a vegan diet, certain medications or past stomach surgery.

Can my psychiatrist order blood work, or do I need my primary care doctor?

Psychiatrists are physicians and can order lab tests. Many coordinate with primary care to avoid duplicate tests and to make sure abnormal results are followed up.

Could my asthma or allergy medicine be affecting my mood?

Montelukast carries an FDA boxed warning about mood and behavior changes. If you take it and notice such changes, the FDA advises stopping it and notifying a health care professional right away. For other medicines, raise your concern with the prescriber before making any change.

Are functional medicine lab panels worth it?

Some are standard tests; others, such as mycotoxin, toxic-metal and leaky-gut panels, are investigational and not validated for diagnosis. Ask what each test can and cannot tell you, and how the result would change your plan, before ordering it.

Sources

1. The American Psychiatric Association Practice Guidelines for the Psychiatric Evaluation of Adults, Third Edition. American Psychiatric Association, 2016. carelonbehavioralhealth.com
2. The PHQ-9: validity of a brief depression severity measure. Journal of General Internal Medicine (Kroenke, Spitzer, Williams), 2001. pmc.ncbi.nlm.nih.gov
3. Hypothyroidism (Underactive). American Thyroid Association, 2026. thyroid.org
4. Hyperthyroidism (Overactive). American Thyroid Association, 2026. thyroid.org
5. Thyroid Dysfunction: Screening. U.S. Preventive Services Task Force, 2015. uspreventiveservicestaskforce.org
6. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239), Recommendations. National Institute for Health and Care Excellence (NICE), 2024. nice.org.uk
7. Anemia - Symptoms. National Heart, Lung, and Blood Institute (NIH), 2026. nhlbi.nih.gov
8. Anemia - Diagnosis. National Heart, Lung, and Blood Institute (NIH), 2026. nhlbi.nih.gov
9. Sleep Apnea - Symptoms. National Heart, Lung, and Blood Institute (NIH), 2026. nhlbi.nih.gov
10. FDA requires Boxed Warning about serious mental health side effects for asthma and allergy drug montelukast (Singulair). U.S. Food and Drug Administration, Drug Safety Communication, 2020. fda.gov
11. Prednisone Tablets, USP prescribing information. DailyMed (National Library of Medicine), 2026. dailymed.nlm.nih.gov
12. Mental Health Issues: Alcohol Use Disorder and Common Co-occurring Conditions. National Institute on Alcohol Abuse and Alcoholism (NIH), Core Resource on Alcohol, 2025. niaaa.nih.gov
13. Guidelines for the evaluation and treatment of perimenopausal depression: summary and recommendations. Menopause (Maki et al.; NAMS and National Network of Depression Centers), 2018. pubmed.ncbi.nlm.nih.gov
14. Canadian ADHD Practice Guidelines, 4.1 Edition. CADDRA - Canadian ADHD Resource Alliance, 2020. adhdlearn.caddra.ca

Educational information, not medical, tax or legal advice. Decisions about diagnosis, medication and treatment belong with a clinician who knows your history.