Summary of diseases and conditions associated with neurotransmitter imbalances, organized by key neurotransmitters.
🔹 1️⃣ Dopamine imbalance
| Imbalance | Associated diseases / conditions | Key features |
| ↓ Dopamine | Parkinson’s disease | Motor deficits (bradykinesia, rigidity, tremor); due to dopaminergic neuron loss in substantia nigra |
| ↓ Dopamine | Depression (motivational deficits) | Anhedonia, low motivation, fatigue |
| ↑ Dopamine | Schizophrenia (mesolimbic pathway) | Positive symptoms (hallucinations, delusions) |
| ↑ Dopamine | Addiction | Excess stimulation of reward pathways |
🔹 2️⃣ Serotonin (5-HT) imbalance
| ↓ Serotonin | Major depressive disorder (MDD) | Low mood, sleep disturbance, anxiety |
| ↓ Serotonin | Anxiety disorders | Excessive worry, panic |
| ↓ Serotonin | Obsessive-compulsive disorder (OCD) | Compulsive behaviors, intrusive thoughts |
| ↑ Serotonin | Serotonin syndrome (toxicity) | Autonomic instability, agitation, neuromuscular hyperactivity |
🔹 3️⃣ Norepinephrine imbalance
| ↓ Norepinephrine | Depression | Fatigue, poor concentration |
| ↑ Norepinephrine | Anxiety, panic disorder | Autonomic hyperarousal (palpitations, tremor) |
| ↑ Norepinephrine | Hypertension | Excess sympathetic tone |
🔹 4️⃣ Acetylcholine imbalance
| ↓ Acetylcholine | Alzheimer’s disease | Memory loss, cognitive decline (loss of cholinergic neurons in basal forebrain) |
| ↓ Acetylcholine | Myasthenia gravis | Autoimmune blockade of ACh receptors at neuromuscular junction → muscle weakness |
| ↑ Acetylcholine | Cholinergic crisis (e.g., organophosphate poisoning) | Salivation, lacrimation, diarrhea, bradycardia, muscle fasciculations, paralysis |
🔹 5️⃣ GABA imbalance
| ↓ GABA | Epilepsy | Seizures due to loss of inhibitory tone |
| ↓ GABA | Anxiety disorders | Restlessness, tension |
| ↓ GABA | Huntington’s disease | Degeneration of GABAergic neurons in striatum → chorea, dementia |
🔹 6️⃣ Glutamate imbalance
| ↑ Glutamate | Excitotoxicity (stroke, TBI) | Neuronal death from excessive glutamate activation of NMDA receptors |
| ↑ Glutamate | Chronic pain | Central sensitization |
| Dysregulated glutamate | Schizophrenia (hypo-NMDA activity theory) | Negative and cognitive symptoms |
🔹 7️⃣ Histamine imbalance
| ↓ Histamine | Excessive sleepiness | Sedative antihistamines block histamine arousal pathways |
| ↑ Histamine | Allergic conditions (peripheral role) | Rhinitis, urticaria |
🔹 8️⃣ Glycine imbalance
| ↓ Glycine | Hyperekplexia (startle disease) | Excessive startle response due to defective glycinergic inhibition in spinal cord |
| ↑ Glycine | Rare glycine encephalopathy (nonketotic hyperglycinemia) | Neonatal seizures, developmental delay
🔹 9️⃣ Endorphins / Substance P imbalance
| ↓ Endorphins | Lower pain threshold | Reduced endogenous analgesia (potential role in fibromyalgia) |
| ↑ Substance P | Enhanced pain transmission | Contributes to chronic pain syndromes |
🔹 Summary table:
| Neurotransmitter | Low levels linked to | High levels linked to |
| Dopamine | Parkinson’s, depression | Schizophrenia, psychosis, addiction |
| Serotonin | Depression, anxiety, OCD | Serotonin syndrome |
| Norepinephrine | Depression | Anxiety, hypertension |
| Acetylcholine | Alzheimer’s, myasthenia gravis | Cholinergic crisis |
| GABA | Epilepsy, anxiety, Huntington’s | — |
| Glutamate | Cognitive impairment (hypofunction) | Excitotoxicity, chronic pain, schizophrenia |
| Histamine | Sedation (antihistamines) | Allergic responses |
| Glycine | Hyperekplexia | Glycine encephalopathy |
| Endorphins | Reduced pain tolerance | — |
| Substance P | — | Chronic pain, hyperalgesia |
✅ Key concept:
- Neurotransmitter imbalances contribute to major neurological, psychiatric, neuromuscular, and autonomic disorders.
- The effect depends on which system is affected (CNS, PNS, autonomic) and the balance between excitatory and inhibitory signaling.