The National Institutes of Health estimates that 5.7 million adults in America suffer from bipolar disorder. Also known as manic-depressive disorder, bipolar disorder is a mental illness characterized by cycles of extreme mood swings between mania and depression. Lithium is a prescription drug used to treat bipolar disorder. It is often referred to as a mood stabilizer or an anti-manic drug.
Function
Despite its long history in the treatment of bipolar disorder, it is not clear exactly how lithium works. Many theories exist on the function of lithium in bipolar disorder. It may exert its affect either by altering electrolytes, neurotransmitters or enzymes in the central nervous system. Its affect on enzymes appears to be the most likely mechanism of action, but it is possible that all three mechanisms work together.
Electrolytes
Lithium shares many of the same properties as sodium. Sodium ions help nerve cells conduct nerve signals. Lithium alters the transport of sodium into the nerve and muscle cells. This would decrease the conductivity of the nerve cells.
Neurotransmitters
Another way lithium exerts its effects is by altering the way the body breaks down neurotransmitters. It appears to increase the effect of serotonin, a neurotransmitter that plays a role in stabilizing moods. Lithium also decreases the levels of the neurotransmitters norepinephrine and dopamine, and prevents the nerve receptors from becoming overly sensitive to the effects of dopamine. The action of lithium on dopamine and norepinephrine reduces mania.
Lithium on Enzymes
According to the textbook Basic and Clinical Pharmacology, the effect of lithium on enzymes in the central nervous system is the most likely explanation for its usefulness in bipolar disorder. Lithium blocks the action of enzymes responsible for the formation of inositol phosphates. This sets in motion a cascade of reactions that affects brain chemistry.
Side Effects
Lithium reduces the action of vasopressin and thyroid-stimulating hormone. Vasopressin is the hormone that regulates the water levels in the body. Thyroid-stimulating hormone causes the thyroid gland to release thyroid hormone, the hormone that regulates metabolism. This may explain why people taking lithium commonly experience increased thirst and urination and low thyroid levels.
The dose required for lithium to work is very close to the toxic dose. People taking lithium should have regular blood tests to make sure their lithium levels remain at a safe level.
Tremor is one of the most common side effects of lithium. Lithium can also cause water retention and swelling.
References
- National Institutes of Health: Mental Health Statistics
- U.S. Pharmacist: Pharmacotherapy for Bipolar Disorder
- Basic and Clinical Pharmacology; Bertram Katzung; 2007
