Rush's Thunderbolts: Calomel, the Mercury Laxative of Early America

For most of the eighteenth and nineteenth centuries, a doctor faced with a fever, a sluggish liver, or a patient who had not “had a passage” for several days was likely to reach for the same white powder. Calomel, a compound of mercury, was a laxative, a purge, and for many physicians close to a universal remedy. It traveled in military medicine chests, in family remedy boxes, and in the saddlebags of the first United States expedition to cross the continent. It also left a trace that archaeologists can still detect.

This is a short history of the mercury laxative: what calomel was, why physicians trusted it, how one Philadelphia doctor made it famous, and how it was finally challenged.

A milder mercury

Calomel is mercurous chloride, written Hg2Cl2. Chemists of the early modern period could make the more dangerous mercuric chloride from mercury ore, and then, by heating that salt with more mercury, produce calomel. Because calomel dissolves far less readily than mercuric chloride, it is less toxic, but it still emptied the bowels, which is what physicians wanted from it.¹ The name is usually traced to Greek words for “good” and “black,” though the powder itself is white.¹

Less toxic did not mean safe. Taken repeatedly, as it often was, calomel produced heavy salivation, inflamed gums, and neurological symptoms such as tremor and changes in personality.¹

Why did a drug like this keep its reputation for so long? Joe Schwarcz of McGill University’s Office for Science and Society offers several reasons: many illnesses clear up on their own and the drug got the credit; belief in a remedy can make patients feel better; and those who died of the treatment could not report on it.¹ Behind all this lay a widely shared belief that laxatives and purgatives removed contagion from the body.²

“Ten and ten”: Benjamin Rush and the 1793 epidemic

The physician who did the most to make calomel an American staple was Benjamin Rush of Philadelphia, a signer of the Declaration of Independence and, in the National Park Service’s words, the leading physician in the United States at the time.² His own account of the yellow fever epidemic that struck Philadelphia in 1793, published the following year, explains how he arrived at his famous purge.

Rush wrote that he suspected his early attempts to clear the bile from fever patients had failed because his purges were too feeble. He remembered that during the Revolutionary War he had seen Dr. Thomas Young, a senior army hospital surgeon, give calomel combined with jalap (a purgative root) for bilious fever, in doses of ten grains of each. The surgeons knew this mixture, Rush wrote, “by simple name of ten and ten.”³ He added the jalap because “calomel is slow in its operation, more especially when it is given in large doses,” and when ten grains of jalap proved too weak he raised it to fifteen. His final prescription was three doses, each of fifteen grains of jalap and ten of calomel, one every six hours until the bowels had moved four or five times.³

Rush described one early patient, a blockmaker named Richard Spain, as surviving after taking eighty grains of calomel over three days, and called him “the first fruits of the efficacy of mercurial purges in the yellow fever.”³ He gave the prescription to the College of Physicians on September 3 and told his fellow citizens that the disease was “no longer incurable.”³ Later in the epidemic, when even calomel and jalap failed to move his patients’ bowels, he substituted gamboge, another strong purgative, and gave a purge every day while the fever lasted.³

Purging was only half of Rush’s method. He paired it with bloodletting, cool air, cold drinks and a low diet, all meant to reduce what he saw as excess stimulation in the body.³ Rush’s confidence rested on his own case reports, not on any comparison with untreated patients. Modern readers know what he did not: yellow fever is a viral disease that neither purging nor bleeding can cure.

Fifty dozen pills for the Corps of Discovery

Rush’s purge did not stay in Philadelphia. When Meriwether Lewis prepared for the expedition to the Pacific in 1803, he met Rush in Philadelphia, received some limited medical instruction, and took with him about 600 of “Rush’s Bilious Pills,” also called “Rush’s Thunderbolts.” According to the National Park Service, the pills combined calomel and jalap, the same pairing Rush had used in 1793, and the captains gave them “almost as a cure-all.”² The chest also held Peruvian bark, opium and laudanum, the opium tincture that a later generation of patients would come to depend on.² (For one such patient, see our article on Elizabeth Barrett Browning and laudanum.)

The journals show the pills in steady use. At Fort Mandan in March 1805, Clark recorded that a visitor the journal calls “the Coal” came with a sick child, “to whome I gave Some of rushes Pills.”⁴ In July 1805, near the Three Forks of the Missouri, Clark arrived in camp with a high fever and aching muscles. Lewis wrote that Clark “thought himself somewhat bilious and had not had a passage for several days,” and that “I prevailed on him to take a doze of Rushes pills, which I have always found sovereign in such cases.” Clark’s own entry is shorter: “take 5 of rushes pills & bathe my feet & legs in hot water.”⁴

The logic of the purge could run in odd directions. In late September 1805, after the expedition had come down from the mountains west of Travelers’ Rest, many of the men fell ill. Clark wrote that they “all Complain of a Lax & heaviness at the Stomack,” a lax being loose bowels, and yet “I gave rushes Pills to the Sick this evening.”⁴ At Fort Clatsop the following February, when Gibson, one of the men, had a stubborn fever, the captains gave him a dose of the pills, which, in Clark’s words, “in maney instancis I have found extreamly efficasious in fevers which are in any measure Caused by the presence of boil.”⁴ The fever eased that night, and the journals give the credit to the pills and to nitre, which had made Gibson sweat.⁴

Mercury also had a second use on the expedition. The National Park Service notes that venereal disease was treated with balsam of copaiba combined with calomel,² and in March 1806 Lewis recorded that two men had recovered and that he “directed them to desist from the uce of mercury.”⁴

A chemical trail at Travelers’ Rest

Most of the expedition’s hundreds of camps left nothing that can be found today. One exception is Travelers’ Rest, near present-day Lolo, Montana, where the captains named a creek in September 1805 and rested before crossing the mountains.⁴ They camped there again on the return journey, from June 30 to early July 1806, while planning to divide the party.⁴

Mercury does not decompose. When archaeologists searched the site, they were looking for the kind of trace a group dosing itself with mercury compounds would leave behind.⁵ In the summer of 2002, excavations turned up fire hearths, lead from gun repairs, and “a trench latrine tainted with mercury.”⁶ The National Park Service explains that researchers combined the mercury signature with journal entries, maps, and a military guidebook the captains used to confirm that this was the expedition’s camp.⁵ Travelers’ Rest is now described as the only archaeologically verified campsite of the expedition.⁶

Two cautions apply. First, the mercury confirms that mercury medicines were used at the spot, not which ones: Rush’s pills are the obvious candidate, but the journals show calomel was also given for venereal disease. Second, the place was not empty before 1805. Travelers’ Rest lies in the traditional homeland of the Salish people, and Pend d’Oreille and Nez Perce peoples also used it as a campsite and trail junction for centuries.⁶ The latrine identifies one short visit to a much older crossroads.

Hammond’s ban

By the Civil War, calomel was still standard army issue, and some physicians had begun to see what it did to patients when it was given freely. On May 4, 1863, Surgeon General William A. Hammond issued an order striking both calomel and tartar emetic (an antimony compound used to cause vomiting) from the army’s supply table. The order, reprinted in the Buffalo Medical and Surgical Journal, said that calomel had “so frequently been pushed to excess by military surgeons” that it had produced “innumerable cases of profuse salivation” and “the not unfrequent occurrence of mercurial gangrene,”⁷ a destructive condition that could disfigure the body.⁸ No further requisitions were to be approved. Hammond closed bluntly: “No doubt can exist that more harm has resulted from the misuse of both these agents, in the treatment of disease, than benefit from their proper administration.”⁷

The order, known as Circular No. 6, cost Hammond popularity among a large segment of the medical profession.⁹ Hammond also had a powerful enemy in Secretary of War Edwin Stanton,⁹⁸ and in 1864 he was court-martialed on charges unrelated to calomel and dismissed from the service.⁹ Historians present the circular as one of the controversies that cost him the support he needed, not as the formal cause of his dismissal.⁹ An undergraduate poster abstract presented at the American Historical Association in 2026 states that calomel returned to the army supply table in 1864 and stayed in use for the rest of the war.⁸

A long decline

Hammond’s order did not end the mercury laxative, even in the army,⁸ and mercury preparations remained in civilian use. “Blue mass,” or the blue pill, was another common mercury preparation; its main ingredient was finely dispersed elemental mercury. In 2001 three medical researchers argued that Abraham Lincoln took blue mass before his presidency, that its mercury may explain some of his behavior in those years, and that he stopped taking it soon after his inauguration.¹⁰ That argument is a hypothesis built on recreating the recipe and on the testimony of Lincoln’s contemporaries. It remains an unproven hypothesis, not a settled diagnosis.¹⁰

What changed in the end was not a single ban but a new understanding of disease. As fevers came to be traced to specific infections, the old idea that a violent purge could carry illness out of the body lost its foundation, and with it went the main reason for giving mercury by mouth.

The history of calomel is easy to tell as a story of foolish doctors, but the sources suggest something less comfortable. Rush, Lewis and Clark all wrote about the pills with sincere confidence, and they kept records of patients who got better. What they lacked was a way to tell recovery that followed the medicine from recovery caused by it. Hammond’s order stands out because it looked at the army’s own records and concluded, in an official document, that the harm outweighed the benefit. The mercury in a Montana latrine is a reminder of how long it took for that conclusion to take hold.

Footnotes

1. Schwarcz, “A Little Mercurial History,” McGill OSS, 2019. ↩ ↩² ↩³ ↩⁴

2. NPS, “Medicine on the Lewis and Clark Expedition.” ↩ ↩² ↩³ ↩⁴ ↩⁵

3. Rush 1794, pp. 199-202 and following (purging and other remedies). ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

4. Journals, Project Gutenberg #8419: entries of March 7, July 27, September 9 and 24, 1805; February 15-16, March 8, June 30 and July 1, 1806. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

5. NPS, “Historic Latrines Help Archeologists Retrace the Lewis and Clark Trail.” ↩ ↩²

6. NPS, “Travelers’ Rest State Park.” ↩ ↩² ↩³

7. Hammond, order of May 4, 1863, in Buffalo Medical and Surgical Journal 2 (1863): 354. ↩ ↩²

8. Phillips, AHA 2026 undergraduate poster abstract, “Calomel Through the Career of William A. Hammond.” ↩ ↩² ↩³ ↩⁴

9. Blustein, “Hammond, William Alexander,” American National Biography, via House Divided. ↩ ↩² ↩³ ↩⁴

10. Hirschhorn, Feldman and Greaves 2001, abstract. ↩ ↩²