Long before protein Pop-Tarts and protein gummy candies, Meriwether Lewis and William Clark were protein-maxing their way across America. For more than two years, the explorers survived on a meat-heavy diet that left them battling wicked constipation. Their solution? A powerful laxative made with mercury. They had no idea that their medicine was poisonous—or that the toxic traces they left behind would help archaeologists retrace their journey nearly 200 years later.
A continent on a shoestring
In 1803, the Louisiana Purchase nearly doubled the size of the United States, adding 828,000 square miles for the bargain price of $15 million. That's about $18 per square mile. Of course, nobody bothered consulting the Native Americans who actually lived there. President Thomas Jefferson had dreamed of exploring the continent for decades, and now he wanted to stake America's claim to the Pacific Northwest before another European power got there first.
Jefferson created a special Army unit called the Corps of Discovery, arguably the coolest name in American military history until Space Force came along. He asked Congress for a modest $2,500 to fund the expedition, pitching it as an opportunity to establish new trade routes and trading partners. But Jefferson had a much bigger ambition: an America stretching from sea to shining sea.
Unfortunately, $2,500 wasn't nearly enough. The Army covered the soldiers' wages, but there was no doctor and no money to hire one. Just $55 was allocated for medicine and $224 for food. The rest of their meals would have to come from hunting and fishing. That meant a steady diet of meat, meat, and more meat. And before the expedition even began, Lewis and Clark were already preparing for one particularly unpleasant consequence: constipation.
Thirty-three souls and a dog
Leading the expedition was Army Captain Meriwether Lewis, Thomas Jefferson's personal secretary, who served as the group's scientist, documenting everything from geography and wildlife to the Native American tribes they encountered. His second-in-command was William Clark, a seasoned military veteran who had retired to his family's Kentucky plantation at just 26 years old. Although the Secretary of War refused to promote Clark to captain, Lewis treated him as an equal. Clark handled the maps and led the hunting parties that kept everyone fed.
The Corps of Discovery was an unlikely collection of soldiers, explorers, and civilians. Among them were French-Canadian trapper Toussaint Charbonneau, his Shoshone wife Sacagawea, and their infant son Jean Baptiste, who wasn't even six months old when the expedition resumed its journey west. There was York, a man enslaved by Clark, German-born miller John Potts, and Pierre Cruzatte, a one-eyed fiddle player of French and Omaha ancestry. And rounding out this extraordinary traveling party was Seaman, Lewis's faithful dog.
The founding father's thunderclappers
The man responsible for stocking Lewis and Clark's medicine chest was no ordinary doctor. Dr. Benjamin Rush was a Founding Father, a signer of the Declaration of Independence, the founder of Dickinson College, and a pioneer of American psychiatry. Before the expedition, Thomas Jefferson sent Lewis to Philadelphia for a crash course in frontier medicine. Rush supplied everything from medicinal wine and Turkish opium to peppermint, Peruvian bark, and 600 of his infamous bilious pills.
Back then, "bilious" was a catch-all diagnosis for everything from nausea to a bad mood. Rush believed most illnesses could be treated by either draining blood or purging the bowels. His enormous pills, roughly four times the size of a modern aspirin, combined powdered jalap root with calomel, a mercury-based compound. Each pill was 50 percent mercury. Rush described their effect as "explosive," earning them the unforgettable nickname "thunderclappers."
Unfortunately, the pills did more than relieve constipation. Prolonged exposure to mercury could cause drooling, mouth sores, bleeding gums, and even tooth loss. Clark's journals paint a grim picture of the expedition's health. Sacagawea became seriously ill and was treated with bloodletting. Other entries describe Captain Lewis as "very sick," nearly all the men falling ill, and York suffering from painful intestinal cramps. Whenever sickness struck, the explorers turned to Rush's pills, never realizing that the medicine they trusted could be making matters worse.
Dr. Rush died in 1813, still convinced that mercury was good medicine. The dangers of prolonged exposure would become increasingly apparent in the decades that followed. Hatmakers who inhaled mercury fumes while turning animal fur into felt developed tremors, personality changes, and hallucinations. Their strange behavior helped popularize the expression "mad as a hatter," later associated with the Mad Hatter in Alice's Adventures in Wonderland. The cruel irony? One of America's most respected physicians had sent Lewis and Clark into the wilderness carrying hundreds of pills containing a dangerous poison.
Lewis and Clark carried 600 laxative pills that were half mercury. Because mercury never breaks down, archaeologists can still find the expedition's campsites by testing its latrines.
What the latrines remember
Mercury doesn't break down, which meant Lewis and Clark were leaving behind more than footprints as they crossed the American wilderness. The Corps of Discovery stopped at least 600 times, and every camp latrine became a potential mercury deposit. Following military guidelines, the men arranged their camps in predictable patterns, with cooking fires and latrines positioned at specific distances from one another.
Nearly 200 years later, archaeologists at Travelers' Rest near Lolo, Montana, discovered something remarkable. In 2002, they identified a pit whose size and distance from old fire hearths matched military camp guidelines. Historical archaeologist Daniel Hall suspected it might contain traces of Dr. Rush's mercury-laced laxatives. Tests confirmed his theory. The poisonous medicine had left behind a chemical fingerprint that survived for two centuries.
It was here that William Clark had once gazed toward the Bitterroot Mountains, exhausted and miserable, writing that he'd been as wet and cold as at any point in his life. Now, thanks to the mercury buried in an ancient latrine, Travelers' Rest became just the second confirmed campsite of the Lewis and Clark Expedition, joining Pompey's Pillar near Billings, Montana. One of the greatest journeys in American history had been traced, in part, through poisonous poop.
The inn outside Nashville
After 28 grueling months and 8,000 miles, the Corps of Discovery returned to St. Louis on September 23, 1806. Remarkably, they'd lost just one man along the way: Sergeant Charles Floyd, who died from a ruptured appendix. William Clark went on to live to 68, an impressive age for the time, especially considering how much mercury he may have consumed.
Meriwether Lewis wasn't so fortunate. In addition to Dr. Rush's infamous pills, he'd taken mercury to treat recurring bouts of malaria. By 1809, the celebrated explorer was struggling with debt, heavy drinking, and deteriorating mental health. Friends described him as melancholy, suspicious, and paranoid. He was reportedly haunted by his failure to discover the legendary Northwest Passage, despite having accomplished one of the most extraordinary expeditions in American history.
In October 1809, Lewis stopped at an inn roughly 70 miles southwest of Nashville, Tennessee. That night, the innkeeper's wife, Priscilla Grinder, heard gunshots. Lewis was discovered with devastating wounds to his head and abdomen. By sunrise, the 35-year-old explorer was dead. Contemporary newspaper accounts reported that he'd attempted to take his own life with a gun before cutting his throat.
Was it suicide or murder? Some believed Lewis had been robbed and killed, pointing to the money he was carrying and his reputation as an expert marksman. But Lewis had reportedly attempted suicide before, prepared his will, and made arrangements for his belongings. Both Thomas Jefferson and William Clark accepted that he'd taken his own life. What neither could have understood was the potential toll of years of mercury exposure. Some modern researchers suspect the toxic medicine may have worsened the depression, paranoia, and mental distress that plagued his final months. Whether mercury played a significant role in his death remains an unanswered question.
Legend has it that Lewis's faithful dog, Seaman, refused to leave his master's grave. Whether that story is true or not, the expedition's legacy is extraordinary. Thirty-three people ventured into an unforgiving wilderness, battling hunger, illness, freezing temperatures, and dangers they could scarcely imagine. They returned having mapped thousands of miles of territory, documented unfamiliar wildlife, and changed the course of American history. And through it all, they were unknowingly swallowing a poison they believed would keep them alive.
