Lugol's iodine, also known as Lugol's solution, first made in 1829, is a solution of elemental iodine and potassium iodide in water, named after the French physician J.G.A. Lugol. Lugol's iodine solution is often used as an antiseptic and disinfectant, for emergency disinfection of drinking water, and as a reagent for starch detection in routine laboratory and medical tests. These uses are possible since the solution is a source of effectively free elemental iodine, which is readily generated from the equilibration between elemental iodine molecules and triiodide ion in the solution.
It has been used more rarely to replenish iodine deficiency. However, pure potassium iodide, containing the relatively benign iodide ion without the more toxic elemental iodine, is strongly preferred for this purpose. Likewise, in the Chernobyl disaster some Lugol's solution was used as an emergency source of iodide to block radioactive iodine uptake, simply because it was widely available as a drinking water decontaminant, and pure potassium iodide without iodine (the preferred agent) was not available.
Formula and manufacture 
Lugol's solution is available in different potencies of 1%, 2%, or 5% Iodine. The 5% solution consists of 5% (wt/v) iodine (I2) and 10% (wt/v) potassium iodide (KI) mixed in distilled water and has a total iodine content of 126.5 mg/mL. Potassium iodide renders the elementary iodine soluble in water through the formation of the triiodide (I−
3) ion. It is not to be confused with tincture of iodine solutions, which consist of elemental iodine, and iodide salts dissolved in water and alcohol. Lugol's solution contains no alcohol.
Other names for Lugol's solution are I2KI (iodine-potassium iodide); Markodine, Strong solution (Systemic); and Aqueous Iodine Solution BCP.
Lugol's is obtained over the counter from drug stores or health food stores. This indicator, also called a stain, is used in many different fields.
- As a mordant when performing a Gram Stain. It is applied for 1 minute after staining with crystal violet, but before ethanol to ensure that gram positive organisms' peptidoglycan remains stained, easily identifying it as a gram positive in microscopy.
- This solution is used as an indicator test for the presence of starches in organic compounds, with which it reacts by turning a dark-blue/black. Elemental iodine solutions like Lugol's will stain starches due to iodine's interaction with the coil structure of the polysaccharide. Starches include the plant starches amylose and amylopectin and glycogen in animal cells. Lugol's solution will not detect simple sugars such as glucose or fructose. In the pathologic condition amyloidosis, amyloid deposits (i.e., deposits that stain like starch, but are not) can be so abundant that affected organs will also stain grossly positive for the Lugol reaction for starch.
- It can be used as a cell stain, making the cell nuclei more visible and for preserving phytoplankton samples.
- During colposcopy, Lugol's iodine is applied to the vagina and cervix. Normal vaginal tissue stains brown due to its high glycogen content, while tissue suspicious for cancer does not stain, and thus appears pale compared to the surrounding tissue. Biopsy of suspicious tissue can then be performed. This is called a Schiller's Test.
- Lugol's iodine may also be used to better visualize the mucogingival junction in the mouth. Similar to the method of staining mentioned above regarding a colposcopy, alveolar mucosa has a high glycogen content that gives a positive iodine reaction vs. the keratinized gingiva.
- Lugol's solution can also be used in various experiments to observe how a cell membrane uses osmosis and diffusion.
- Lugol's iodine may also be used as an oxidizing germicide, however it is somewhat undesirable in that it may lead to scarring and discolors the skin temporarily. One way to avoid this problem is by using a solution of 70% ethanol to wash off the iodine later.
- Lugol's solution is also used in the marine aquarium industry. Lugol's solution provides a strong source of free iodine and iodide to reef inhabitants and macroalgae. Although the solution is thought to be effective when used with stony corals, systems containing xenia and soft corals are assumed to be particularly benefited by the use of Lugol's solution. Used as a dip for stony and soft or leather corals, Lugol's may help rid the animals of unwanted parasites and harmful bacteria. The solution is thought to foster improved coloration and possibly prevent bleaching of corals due to changes in light intensity, and to enhance coral polyp expansion. The blue colors of Acropora spp. are thought to be intensified by the use of potassium iodide. Specially packaged supplements of the product intended for aquarium use can be purchased at specialty stores and online.
- Preoperative administration of Lugol's solution decreases intraoperative blood loss during thyroidectomy in patients with Grave's disease. However, it appears ineffective in patients who are already euthyroid on anti-thyroid drugs and levothyroxine.
Historical applications 
Lugol's was often used in the treatment of gout.
It was also used at one time as a first line treatment for hyperthyroidism, as the administration of pharmacologic amounts of iodine leads to temporary inhibition of iodine organification in the thyroid gland, a phenomenon called the Wolff-Chaikoff effect. However it is not used to treat certain autoimmune causes of thyroid disease as iodine-induced blockade of iodine organification may result in hypothyroidism. They are not considered as a first line therapy because of possible induction of resistant hyperthyroidism but may be considered as an adjuvant therapy when used together with other hyperthyrodism medications.
Because of its wide availability as a drinking-water decontaminant, and high content of potassium iodide, emergency use of it was at first recommended to the Polish government in 1986, after the Chernobyl disaster to replace and block any intake of radioactive 131I, even though it was known to be a non-optimal agent, due to its somewhat toxic free-iodine content. Other sources state that pure potassium iodide solution in water (SSKI) was eventually used for most of the thyroid protection after this accident. There is "strong scientific evidence" for potassium iodide thyroid protection to help prevent thyroid cancer. Potassium iodide does not provide immediate protection but can be a component of a general strategy in a radiation emergency.
Historically, Lugol's iodine solution has been widely available and used for a number of health problems with some precautions. Lugol's is sometimes prescribed in a variety of alternative medical treatments.
Until 2007, in the United States of America, Lugol's solution was unregulated and available over the counter as a general reagent, an antiseptic, a preservative, or as a medicament for human or veterinary application.
However, effective August 1, 2007, the DEA now regulates Lugol's solution (and, in fact, all iodine solutions containing greater than 2.2% iodine) as a List I precursor because it may potentially be used in the illicit production of methamphetamine. However, transactions of up to one fluid ounce (30 ml) of Lugol's solution are exempt from this regulation. By contrast, Lugol's iodine solution is available over the counter in Canada and Mexico.
Because it contains free iodine, Lugol's solution at 2% or 5% concentration without dilution is irritating and destructive to mucosa, such as the lining of the esophagus and stomach. Doses of 10 mL of 5% solution have been reported to cause gastric lesions when used in endoscopy.  The lethal dose of free iodine for an adult human of 2 to 3 grams (2000-3000 mg) free iodine represents 40 to 60 mL (less than 2 fluid ounces) of 5% Lugol's solution.
- http://lpi.oregonstate.edu/infocenter/minerals/iodine/ Higdon, J., "Micronutrient Information Center: Iodine," Linus Pauling Institute/Oregon State University; April, 2003 (revised by Drake, V.J., July, 2007).
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- Erbil Y, Ozluk Y, Giriş M, et al. (June 2007). "Effect of lugol solution on thyroid gland blood flow and microvessel density in the patients with Graves' disease". J. Clin. Endocrinol. Metab. 92 (6): 2182–9. doi:10.1210/jc.2007-0229. PMID 17389702.
- Kaur S, Parr JH, Ramsay ID, Hennebry TM, Jarvis KJ, Lester E (May 1988). "Effect of preoperative iodine in patients with Graves' disease controlled with antithyroid drugs and thyroxine". Ann R Coll Surg Engl 70 (3): 123–7. PMC 2498739. PMID 2457351.
- Rotkiewicz, Marcin; Henryk Suchar and Ryszard Kamiñski (14 January 2001). "Chernobyl: the Biggest BLUFF of the 20th Century". Polish weekly Wprost. pp. no 2. Retrieved 2008-06-18.
-  US FDA, "Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies," U.S. Department of Health and Human Services Food and Drug Administration Center for Drug Evaluation and Research (CDER); December, 2001.
- "Iodine." MedlinePlus.
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-  Hawkins et al., "Change in cyanobacterial biovolume due to preservation by Lugol's Iodine," Harmful Algae, Volume 4, Issue 6, pp. 1033-1043; November, 2005.
-  US DEA, "Final Rule: Changes in the Regulation of Iodine Crystals and Chemical Mixtures Containing Over 2.2 Percent Iodine," Federal Register, Volume 72, Number 126; July 2, 2007 (FR Doc E7-12736).
-  Direct toxicity of Lugol's solution.