DMSA, short for dimercaptosuccinic acid, is a medication used to treat heavy metal poisoning. Sold under the brand name Chemet, it works by binding to toxic metals like lead, mercury, and arsenic in the body so they can be flushed out through urine. It’s the most commonly prescribed chelation drug in American healthcare today, largely because it can be taken by mouth rather than given by injection.
How DMSA Removes Heavy Metals
DMSA belongs to a class of drugs called chelators, from the Greek word for “claw.” The molecule has two sulfur-containing groups (called thiol groups) that grab onto metal atoms in the bloodstream, forming a stable complex that the kidneys can then filter out. Different metals attach to DMSA in slightly different ways. Lead and cadmium bond to one sulfur atom and one oxygen atom on the molecule, while mercury bonds to both sulfur atoms. For arsenic, DMSA essentially outcompetes the body’s own proteins for binding the metal, pulling it away from tissues where it causes damage.
Once DMSA latches onto a metal, the complex travels through the bloodstream to the kidneys. The body eliminates both the drug and the bound metal in urine. In healthy adults, the drug has a half-life of about 2 hours, meaning half of it clears the body in that time. In children with lead poisoning, the half-life is somewhat longer, around 3 hours, and kidney clearance of the drug is slower compared to healthy individuals.
FDA-Approved Use: Childhood Lead Poisoning
DMSA is FDA-approved for one specific purpose: treating lead poisoning in children aged 1 year and older whose blood lead levels exceed 45 micrograms per deciliter. This is a significantly elevated level, well above the point where health effects become concerning.
A standard treatment course follows a specific schedule. Children receive 10 mg per kilogram of body weight every 8 hours for the first 5 days, then every 12 hours for an additional 14 days. That’s a 19-day course in total. If blood lead levels remain high after treatment, the course can be repeated, typically after waiting at least 2 weeks. Some treatment plans extend the overall course to 21 or 28 days depending on the situation.
One of DMSA’s key advantages is that it’s relatively selective. Compared to older chelation drugs, it causes minimal loss of essential minerals like zinc, iron, and calcium, which the body needs. This matters especially in children, where depleting essential nutrients could cause its own set of problems.
Off-Label Uses: Mercury and Arsenic
Though not FDA-approved for these purposes, DMSA is also used to treat mercury and arsenic poisoning. These are considered off-label uses, meaning physicians prescribe it based on clinical evidence and judgment even though the drug’s formal approval only covers lead.
For mercury, DMSA does increase the amount of mercury excreted in urine. In one study of people with mercury exposure, average 24-hour urinary mercury excretion rose from 4.3 micrograms to 7.8 micrograms after a DMSA dose, roughly doubling output. However, the same study found that DMSA challenge testing wasn’t useful for detecting mercury exposure that happened years earlier, since the drug can only pull out metal that’s still accessible in the body.
The Chelation Challenge Test Controversy
Some practitioners use DMSA in a “provoked” or “challenge” urine test. The idea is to give a dose of DMSA, collect urine afterward, and use the metal levels in that urine to diagnose heavy metal toxicity. This practice is controversial, and major medical organizations have taken a firm stance against it.
The American College of Medical Toxicology issued a position statement disapproving of post-chelation challenge urine testing entirely. Their reasoning is straightforward: no scientifically accepted normal reference values exist for urine metals collected after a chelation dose. Of course urine metal levels rise after giving a drug designed to pull metals out of the body. Without knowing what “normal” looks like under those artificial conditions, the results can’t meaningfully distinguish a sick person from a healthy one. The ACMT concluded that the practice “has not been scientifically validated, has no demonstrated benefit, and may be harmful” when used to guide treatment decisions.
If you’ve had this type of test and were told your results show toxic metal levels, it’s worth knowing that the standard, validated approach to checking for metal exposure is a simple blood or unprovoked urine test, not one done after taking a chelation drug.
Side Effects and Safety
DMSA is considered one of the safer chelation drugs available, but it’s not without side effects. The most commonly reported issues are gastrointestinal: nausea, vomiting, diarrhea, and loss of appetite. Some patients experience a sulfurous odor in their urine or breath, which is harmless but noticeable. Mild elevations in liver enzymes have been reported, as have occasional allergic reactions. Rashes can occur, and in rare cases they may be severe enough to require stopping treatment.
During treatment, blood counts and liver function are typically monitored to catch any problems early. The drug has not been established as safe for infants under 12 months old.
How DMSA Compares to Other Chelators
Several chelation drugs exist, each with different strengths and limitations. DMSA’s main practical advantage is that it’s taken as a capsule by mouth, making it far easier to use than alternatives that require injections or IV infusions.
- BAL (dimercaprol): An older chelation drug approved for arsenic, gold, and mercury poisoning. It must be given by deep intramuscular injection mixed with peanut oil, making it painful and impractical for outpatient use. It’s also used alongside another chelator for acute lead poisoning.
- Calcium disodium EDTA: Approved for lead poisoning but only available as an injection. Supply shortages have been an ongoing issue, and there is no FDA-approved oral version.
- DMPS: Structurally similar to DMSA and available in both oral and intravenous forms. It’s used for mercury and arsenic poisoning but is not FDA-approved in the United States. It can sometimes be obtained through compounding pharmacies.
- Penicillamine: An oral chelator approved for Wilson’s disease (a copper storage disorder) and sometimes used off-label for lead. It has only one thiol group compared to DMSA’s two, making it generally less effective at grabbing heavy metals.
For most cases of lead poisoning in children that don’t require hospitalization, DMSA is the first-line choice precisely because it works by mouth, has a relatively mild side effect profile, and doesn’t strip the body of essential minerals the way some older chelators can.