- Macular Degeneration
- Mad Cow Disease see Creutzfeldt-Jakob Disease
- Magnesium see Minerals
- Magnetic Resonance Imaging see MRI Scans
- Makeup see Cosmetics
- Malabsorption Syndromes
- Malaria
- Male Breast Cancer
- Male Genital Disorders see Penis Disorders; Testicular Disorders
- Male Infertility
- Male Menopause see Men's Health
- Male Sterilization see Vasectomy
- Malignancy see Cancer
- Malnutrition
- Mammaplasty see Breast Reconstruction
- Mammography
- Man-Made Disasters see Biodefense and Bioterrorism; Chemical Emergencies; Radiation Emergencies
- Managed Care
- Mandibular Disorders see Jaw Injuries and Disorders
- Manic-Depressive Illness see Bipolar Disorder
- Maple Syrup Urine Disease see Genetic Brain Disorders
- Marfan Syndrome
- Marijuana
- Mastectomy
- Maternal Health see Postpartum Care
- Maxillary Disorders see Jaw Injuries and Disorders
- MCI see Mild Cognitive Impairment
- MDMA see Club Drugs
- MDS see Myelodysplastic Syndromes
- Measles
- Mediastinal Disorders see Chest Injuries and Disorders
- Medicaid
- Medical Device Safety
- Medical Ethics
- Medical Professions see Health Occupations
- Medical Research see Understanding Medical Research
- Medicare
- Medication Errors
- Medicinal Herbs see Herbal Medicine
- Medicines
- Medicines and Children
- Medicines and Pregnancy see Pregnancy and Medicines
- Medicines, Over-the-Counter see Over-the-Counter Medicines
- Mediterranean Anemia see Thalassemia
- Melanoma
- Memory
- Men's Health
- Meniere's Disease
- Meningioma see Brain Tumors
- Meningitis
- Meningococcal Disease
- Meningococcal Infections see Meningococcal Disease
- Meningococcemia see Meningococcal Disease
- Meniscus see Knee Injuries and Disorders
- Menopausal Hormone Therapy see Hormone Replacement Therapy
- Menopause
- Menopause, Male see Men's Health
- Menstruation
- Mental Disorders
- Mental Health
- Mental Health, Child see Child Mental Health
- Mental Health, Older Adults see Older Adult Mental Health
- Mental Health, Teen see Teen Mental Health
- Mental Retardation see Developmental Disabilities
- Mercury
- Merkel Cell Cancer see Skin Cancer
- Mesothelioma
- Metabolic Disorders
- Metabolic Syndrome
- Methadone see Pain Relievers
- Methamphetamine
- Methicillin Resistant Staphylococcus Aureus see MRSA
- MI see Heart Attack
- Micturition see Urine and Urination
- Migraine
- Mild Cognitive Impairment
- Military Health see Veterans and Military Health
- Milk Allergy see Food Allergy
- Milk Intolerance see Lactose Intolerance
- Minerals
- Mini-Stroke see Transient Ischemic Attack
- Miscarriage
- Mitochondrial Diseases
- Mitral Valve Prolapse
- Mixed Connective Tissue Disease see Connective Tissue Disorders
- Mobility Aids
- Molar Pregnancy see Tumors and Pregnancy
- Molds
- Moles
- Molluscum Contagiosum see Skin Infections
- Moniliasis see Yeast Infections
- Monkeypox see Mpox
- Mono see Infectious Mononucleosis
- Mononucleosis see Infectious Mononucleosis
- Mood Disorders
- Morphea see Scleroderma
- Morton's Neuroma see Foot Injuries and Disorders
- Mosquito Bites
- Motion Sickness
- Motor Vehicle Safety
- Mouth Cancer see Oral Cancer
- Mouth Disorders
- Movement Disorders
- Mpox
- MRI Scans
- MRSA
- MS see Multiple Sclerosis
- Mucocutaneous Lymph Node Syndrome see Kawasaki Disease
- Mucolipidoses see Metabolic Disorders
- Mucopolysaccharidoses see Carbohydrate Metabolism Disorders
- Multifocal Atrial Tachycardia see Arrhythmia
- Multiple Births see Twins, Triplets, Multiple Births
- Multiple Endocrine Neoplasia see Endocrine Diseases; Parathyroid Disorders
- Multiple Myeloma
- Multiple Sclerosis
- Multiple System Atrophy see Autonomic Nervous System Disorders
- Mumps
- Muscle Cramps
- Muscle Disorders
- Muscle Strain see Sprains and Strains
- Muscular Dystrophy
- Myalgic Encephalomyelitis/Chronic Fatigue Syndrome
- Myasthenia Gravis
- Mycobacterial Infections
- Mycoses see Fungal Infections
- Myelodysplastic Syndromes
- Myelomeningocele see Spina Bifida
- Myeloproliferative Disorders see Bone Marrow Diseases
- Myocardial Infarction see Heart Attack
- Myopathies see Muscle Disorders
- Myopia see Refractive Errors
- Myositis