What is lithium as medicine? How does it interact with other drugs?

Inositol

Effect: Possible Helpful Interaction

Lithium may cause or exacerbate symptoms of psoriasis.
One small, double-blind study found that the use of supplemental inositol may
help alleviate this problem.

Herbal Diuretic

Effect: Possible Harmful Interaction

The use of lithium as a therapy requires careful attention to lithium levels in the blood. If there is too little lithium, the treatment will not work; if lithium levels get too high, toxicity may result.

One cause of excessively high lithium levels is dehydration.
When the amount of water in the blood decreases, lithium levels proportionally
rise. For this reason, persons taking lithium are warned that they must be sure to
drink sufficient liquids when they are exposed to heat. Diuretic
drugs (water pills) can also cause problems, by causing the
body to excrete water.

One case report suggests that herbal diuretics can also lead to increased lithium levels. Certain herbs are thought to act as diuretics, including buchu, celery seed, cleavers, corn silk, couch grass, dandelion, goldenrod, gravel root, horsetail, juniper, parsley, rosemary, and wild carrot.

This report noted the case of a twenty-six-year-old woman who had been taking a constant dose of lithium for five months without any problems. When she suddenly developed drowsiness, tremor, unsteadiness in walking, and rapid involuntary movements of the eyes, doctors conducted a laboratory examination and found that her lithium level had skyrocketed. It turned out that a few weeks before this episode she had started taking an herbal weight-loss formula that included numerous herbal diuretics.

Manufacturers frequently add herbal diuretics to weight-loss formulas to cause short-term loss of water weight. This has no value for long-term weight loss, but it does give some immediate sense of success. However, in this case, the herbal diuretics also caused lithium levels to rise.

Citrate

Effect: Possible Harmful Interaction

Potassium citrate, sodium citrate, and potassium-magnesium citrate are sometimes used to prevent kidney stones. These supplements reduce urinary acidity and can therefore lead to decreased blood levels and effectiveness of lithium.

Allan, S. J., et al. “The Effect of Inositol Supplements on the Psoriasis of Patients Taking Lithium.” British Journal of Dermatology 150 (2004): 966-969.

Pyevich, D., and M. P. Bogenschutz. “Herbal Diuretics and Lithium Toxicity.” American Journal of Psychiatry 158 (2001): 1329.