Mercury in OTC Medicine: Why Did the FDA Ban Mercurochrome and Merthiolate?

For decades, the go-to topical antiseptics for kids with skinned knees, cut elbows or splinters would have been Merthiolate or Mercurochrome. These mercury-containing products were found in almost every medicine chest in America. Parents would often apply these colorful liquids to prevent infection. How effective they were remains controversial. But children were often quite impressed because the distinctive dark red color of Mercurochrome stained the skin and stung when applied to an open wound. Merthiolate had somewhat similar properties. But, like lead, mercury is now recognized as quite toxic.

Mad as a Hatter:

Do you remember the Hatter in the Lewis Carroll books, Alice’s Adventures in W0nderland and Through the Looking-Glass? Most people remember this character as “The Mad Hatter.” What might have turned the hatter “mad?”

One of my pharmacology professors at the University of Michigan School of Medicine told us grad students the back story behind the phrase “mad as a hatter.” Although Lewis Carroll’s books were published in 1865 and 1871, there was a recognition that the hat-making profession was dangerous in the prior century. Hatters often complained of the shakes because of their severe hand tremors. They lurched when they walked. There were many other symptoms including “mental instability” and irritability.

Mercury was the culprit. It was used to make felt hats. Mercuric nitrate softened the animal hair and made it easier to shape. But hatters inhaled mercury in vapors while making felt hats. And that, dear reader, is how the phrase “mad as a hatter” was born.

In fact, one of my mentors at the University of Michigan, Dr. Hank Swain, was a cardiovascular pharmacologist. In those days, researchers used glass tubes filled with mercury to measure blood pressure in animal experiments. If one of those tubes broke, it spilled a lot of liquid mercury everywhere.

Mercury is incredibly hard to clean up because this “liquid silver” or “quicksilver” could hide in nooks and crannies. My professor experienced mercury poisoning because of just such an accident.

Mercury in Over-the-Counter Products:

During the early 20^th century, doctors believed that mercury-containing pharmaceuticals had powerful antibacterial and anti-fungal activity. Eli Lilly obtained the patent on thimerosal in 1928 and marketed it as Merthiolate shortly thereafter.

Thimerosal was also used in nasal sprays, eye wash, diaper rash treatment and vaginal spermicides. Since virtually every household in America had a mercury-containing glass thermometer, there wasn’t much concern about this potentially toxic element.

Mercury in Minamata City, Japan:

A horrifying public health disaster in Japan in the mid-20^th century brought mercury poisoning to the world’s attention. A petrochemical company had polluted Minamata Bay with mercury. People who ate fish and shellfish from the bay accumulated large amounts of methylmercury in their bodies. Nine hundred died, and countless others were permanently disabled (Lancet, Jan. 14, 2006).

Scientists worry about mercury in fish in part because of the Minamata debacle. This environmental disaster created a clear example of how industrial pollution with a heavy metal could wreak havoc on humans. It also taught researchers that toxicity can build up gradually. A great deal of damage can be done before it is detected.

Congress and the FDA Began to Worry About Mercury in Medicine:

Minamata was long ago and far away, but it did start to raise red flags. In 1980 the FDA began reviewing the safety and effectiveness of mercury-containing products. In 1997 Congress passed the Food and Drug Administration Modernization Act. It required the agency to investigate mercury in foods and drugs. Subsequently, in 1998 the FDA banned the use of thimerosal in OTC products.

Congress also expressed concern about the use of mercury in vaccines administered to kids. In 2001, thimerosal was removed from all vaccines for young children. The only vaccines that continued to be preserved with thimerosal were multi-dose vials used for influenza immunization.

Liquid Mercury in Glass Thermometers:

The states also began to recognize that mercury posed a hazard. Glass thermometers broke easily and the mercury that spilled out was difficult to collect. Mercury is liquid at room temperature. People exposed to mercury by breathing, touching or consuming it could experience serious toxicity. Long-term exposure can result in mercury poisoning. Because of these hazards, at least 13 states have forbidden the manufacture or sale of mercury thermometers. In practical terms, mercury thermometers have disappeared.

There is no question that methylmercury is extremely toxic, which is why pregnant women are warned to avoid consuming large fish such as shark, king mackerel, tilefish, swordfish and albacore tuna. Because these fish eat so many smaller fish, they tend to have high levels of methylmercury.

Ethylmercury vs. Methylmercury:

The controversy in 2025 centers on ethylmercury (thimerosal) rather than methylmercury. No one suggests that methylmercury is safe for humans. Minimata taught us that! But scientists have been arguing about the safety of ethylmercury for decades.

Many scientists maintain that ethylmercury isn’t that bad. After all, it was used for almost a century in OTC products. The argument goes that people can eliminate ethylmercury from the body much easier than methylmercury. And researchers have been defending the use of thimerosal as a preservative in vaccines for decades. They insist that the mercury levels in multi-use vaccine vials are so low as to be meaningless.

Others point out that mercury, in any form, is not good for us. It can negatively affect mitochondria, the energy factories in our cells.

Italian scientists have pointed out that (Biological Trace Element Research, Feb. 2019):

“Also, methylmercury can pass through blood-brain and placental barriers, causing serious damage in the central nervous system. This review describes the toxic effects of mercury in cell cultures, in animal models, and in patients with neurodegenerative diseases. In vitro experiments showed that mercury exposure was principally involved in oxidative stress and apoptotic processes. Moreover, motor and cognitive impairment and neural loss have been confirmed in various studies performed in animal models. Finally, observational studies on patients with neurodegenerative diseases showed discordant data about a possible mercury involvement.”

According to the European Medicines Agency, other preservatives may be equally effective against microbes under some conditions. However, the trend is toward eliminating the use of multi-dose vaccine vials and the need for preservatives.

The CDC’s Advisory Committee on Immunization Practices met on June 25, 2025, and called for vaccines to be free of thimerosal going forward. Critics of the committee’s decision worried that not having multi-dose vials available would mean fewer people would be immunized against the flu. But only about 4% of the current flu vaccine supply contains thimerosal. Perhaps it’s time to eliminate all mercury from pharmaceuticals.

What Do You Think About Mercury in Vaccines?

We would appreciate your perspective about mercury. Is this all a tempest in a teapot or would you like to see mercury eliminated from multi-use vaccine vials? This issue has ignited a firestorm of controversy for reasons that are puzzling to us. That’s why we would appreciate your thoughts in the comment section below. If you think this article is worthy of attention, please share it with friends and family.