Several widely available over-the-counter medications can cause life-threatening harm in overdose, and some of them sit in nearly every medicine cabinet. Acetaminophen alone is the leading cause of acute liver failure in many countries, but it shares shelf space with painkillers, antihistamines, cough syrups, antidiarrheals, and even supplements that carry serious overdose risks. In one study at emergency departments in Northern Ireland, OTC drug-related overdoses made up about 40% of all overdose cases.1PubMed. Prevalence of over-the-counter drug-related overdoses at Accident and Emergency departments in Northern Ireland–a retrospective evaluation Because these products don’t require a prescription, many people underestimate their potential to do harm.
Acetaminophen
Acetaminophen (known as paracetamol outside the United States) is probably the single most dangerous OTC drug in overdose. At normal doses, your liver handles it fine. But when too much is taken, the liver’s usual detoxification pathway gets overwhelmed, and a toxic byproduct called NAPQI builds up. NAPQI depletes the liver’s protective stores and starts damaging liver cells directly, particularly by attacking proteins in mitochondria.2PubMed Central. Mechanisms of acetaminophen hepatotoxicity and their translation to the human pathophysiology The result can be fulminant liver failure, which is fatal without a transplant if it progresses far enough.
What makes acetaminophen especially treacherous is how easy it is to take too much without realizing it. The drug hides in dozens of combination products: cold and flu remedies, PM sleep aids, migraine formulas, and sinus tablets. A study examining how adults use non-prescription acetaminophen products found that nearly half of participants demonstrated they would accidentally overdose by taking two acetaminophen-containing products at the same time, a mistake researchers call “double-dipping.”3PubMed Central. Risk of unintentional overdose with non-prescription acetaminophen products Someone fighting a bad cold might take a Tylenol tablet for a headache and then reach for a NyQuil-type product at bedtime, not realizing both contain acetaminophen.
The good news is that there is an effective antidote. Acetylcysteine, given either intravenously or orally, replenishes the liver’s protective stores and can prevent serious injury if administered early enough after the overdose.4PubMed Central. Novel acetylcysteine regimens for treatment of paracetamol overdose The catch is timing: the window for best results is roughly within eight hours of ingestion. People who take a gradual, stacking overdose over several days sometimes show up late because they didn’t realize anything was wrong until liver damage was already advanced.
Aspirin and Other Salicylates
Aspirin overdose is less common than it once was, but it remains dangerous and harder for clinicians to manage than many realize. In overdose, salicylates disrupt the way your cells produce energy, interfering with several metabolic pathways at once. This leads to a distinctive acid-base disturbance where the body simultaneously develops two opposite problems: respiratory alkalosis from hyperventilation, and a worsening metabolic acidosis from acid buildup in the blood.5PubMed Central. Acute Salicylate Toxicity: A Narrative Review for Emergency Clinicians Symptoms progress from ringing in the ears, nausea, and rapid breathing to confusion, seizures, and organ failure in severe cases.
Salicylate toxicity doesn’t come only from swallowing aspirin tablets. Topical pain creams containing methyl salicylate, such as muscle rubs, can deliver enough salicylate through the skin to cause systemic poisoning. One reported case involved a man who developed severe salicylate toxicity from both ingesting and applying methyl salicylate products, reaching a peak blood salicylate level well into the dangerous range. Even after the cream was washed off, his toxicity persisted because the drug continued absorbing from his skin.6PubMed Central. Salicylate toxicity from ingestion and continued dermal absorption This is an unusual route of overdose, but it has caused deaths, and it catches people off guard precisely because they think of a topical product as purely local.
Ibuprofen and Other NSAIDs
Ibuprofen is often thought of as remarkably safe, and at normal doses it generally is. Most ibuprofen overdoses cause little more than nausea and stomach upset. But massive ingestions tell a different story. A case report of a teenager who took roughly 50 grams of ibuprofen describes cardiovascular collapse, kidney failure, lung hemorrhage, and gastric bleeding, requiring extracorporeal membrane oxygenation to keep him alive.7PubMed. Massive ibuprofen overdose requiring extracorporeal membrane oxygenation for cardiovascular support Another case documented an 18-year-old who consumed roughly 100 grams, leading to coma, dangerously low blood pressure, severe coagulopathy, and a deep metabolic acidosis.8Clinical Toxicology. Massive Ibuprofen Ingestion Resulting in Coagulopathy, Hypotension, and Coma without Significant Renal Failure The effects of massive ibuprofen overdose are variable and somewhat unpredictable: one person may develop kidney failure while another with a similar dose does not.
Other NSAIDs carry their own overdose profiles. Mefenamic acid, a prescription NSAID in many countries but available OTC in some, is known for causing seizures at relatively modest overdose levels. A case report described a young woman who developed generalized seizures and acute kidney injury after taking just 2.5 grams, with blood levels confirmed above the toxic threshold.9PubMed Central. Mefenamic Acid Poisoning Revisited: Central Nervous System Toxicity and Acute Kidney Injury The seizure risk with mefenamic acid is substantially higher than with ibuprofen or naproxen, making it especially dangerous in overdose.
Antihistamines
First-generation antihistamines like diphenhydramine (the active ingredient in Benadryl and many OTC sleep aids) are heavily anticholinergic, meaning they block a signaling chemical throughout the body. In overdose, this produces a recognizable syndrome: dry skin, flushed face, dilated pupils, urinary retention, rapid heart rate, agitation, confusion, and hallucinations. But the more serious threat is cardiac. Diphenhydramine in high doses can depress the heart muscle and cause dangerous changes in the heart’s electrical conduction, including widening of the QRS complex and prolongation of the QT interval on an electrocardiogram.10International Journal of Cardiology. QT interval prolongation in diphenhydramine toxicity These electrical disturbances can trigger fatal heart rhythms.
Diphenhydramine is one of the more commonly abused OTC medications, particularly among teenagers and young adults, sometimes under the internet-fueled “Benadryl challenge.” Because it is sold everywhere and perceived as mild, people dramatically underestimate the cardiac risk. Seizures are another common complication in large overdoses. There is no specific antidote for diphenhydramine overdose; treatment is supportive and focuses on managing seizures, stabilizing heart rhythm, and sometimes using sodium bicarbonate to counteract the drug’s effect on cardiac conduction.
Cough Suppressants
Dextromethorphan, the “DM” or “DXM” in cough syrup brands, is widely abused for its dissociative and hallucinogenic effects at high doses. At therapeutic levels, it suppresses the cough reflex. At high doses, it acts on brain receptors in a way that produces effects resembling those of dissociative anesthetics.11PubMed Central. Dextromethorphan abuse Users sometimes describe a progression of “plateaus,” from mild euphoria to full dissociation and loss of motor control.
The danger intensifies when dextromethorphan is combined with other serotonin-affecting drugs, such as certain antidepressants. Dextromethorphan inhibits serotonin reuptake, and when stacked with another serotonergic medication, the combination can precipitate serotonin syndrome, a potentially life-threatening condition involving high fever, muscle rigidity, rapid heart rate, and seizures.11PubMed Central. Dextromethorphan abuse Many cough and cold products also combine dextromethorphan with acetaminophen, antihistamines, or decongestants, so a person trying to get high on DXM by chugging a whole bottle may simultaneously overdose on those other ingredients. The acetaminophen hidden in combination cough syrups has caused liver failure in people who thought they were only overdosing on the cough suppressant.
Loperamide
Loperamide, sold as Imodium and generics, is an opioid that normally stays in the gut and doesn’t cross into the brain at standard doses. But when taken in huge quantities, it can produce both opioid effects (respiratory depression, sedation) and a separate and dangerous cardiac toxicity. Loperamide blocks potassium channels in the heart, prolonging the QT interval and setting up the conditions for a lethal arrhythmia called torsades de pointes. Case reports describe patients developing this arrhythmia after taking large numbers of tablets. In one case, a 34-year-old woman took 48 tablets of 2 mg loperamide and presented with variable heart block and a QT interval of 560 milliseconds that later stretched to 656 ms, triggering torsades de pointes that required defibrillation.12PubMed Central. Loperamide-Induced Torsades de Pointes
Loperamide abuse became a recognized pattern over the past decade, sometimes called “the poor man’s methadone,” as people with opioid use disorder turned to massive doses to self-treat withdrawal or get high. The cardiac toxicity is insidious because naloxone, the standard opioid-reversal drug, can reverse the respiratory depression but does nothing for the heart rhythm abnormality.12PubMed Central. Loperamide-Induced Torsades de Pointes Loperamide’s long half-life means the cardiac effects can persist for days, and the arrhythmias may recur even after initial treatment.13PubMed Central. Loperamide overdose causing torsades de pointes and requiring Impella temporary mechanical support: a case report In response to reports of abuse and death, the FDA asked manufacturers to change the packaging of loperamide to limit the number of doses in a single package.
Laxatives and Antacids
Laxative overdose tends to be chronic rather than a single dramatic event, but the consequences can be just as deadly. Stimulant laxatives and osmotic agents can deplete potassium and other electrolytes over time. A systematic review of case reports found that laxative-induced low potassium was severe in about half of the cases examined, with the resulting electrolyte imbalance capable of causing life-threatening heart rhythm disturbances.14PubMed. Adverse drug event of hypokalaemia-induced cardiotoxicity secondary to the use of laxatives: A systematic review of case reports This pattern is especially common in eating disorders, where laxative misuse can continue for months or years.
Magnesium-containing laxatives carry a separate risk. Excessive use can cause dangerous elevations of blood magnesium, leading to low blood pressure, slowed heart rate, and respiratory failure. One fatal case attributed severe hypotension directly to magnesium toxicity from overuse of OTC laxatives.15The American Journal of the Medical Sciences. Fatal Hypermagnesemia Due to Laxative Use Calcium-based antacids pose a parallel problem. Excessive intake of calcium carbonate products like Tums can trigger milk-alkali syndrome, a triad of high blood calcium, metabolic alkalosis, and acute kidney injury.16PubMed Central. A Case Report of Milk-Alkali Syndrome Secondary to Excessive Antacid Use Some patients develop this syndrome while combining calcium antacids with vitamin D supplements, which increases calcium absorption and accelerates the problem. One such case documented kidney function dropping to a critically low estimated filtration rate with dangerously elevated calcium and magnesium levels.17American Journal of Kidney Diseases. Calcium-Alkali Syndrome Due to Vitamin D Administration and Magnesium Oxide Administration
Iron Supplements
Iron tablets are one of the oldest-known causes of fatal poisoning from an OTC product, particularly in children. In adults who take a massive dose deliberately, iron causes severe gastrointestinal bleeding as it corrodes the lining of the stomach and intestines, followed by fulminant liver failure as free iron overwhelms the body’s ability to bind and store it safely. A report of two young adults who deliberately consumed large quantities of iron tablets describes exactly this progression: devastating GI hemorrhage followed by liver failure within 48 hours.18PubMed Central. Fatal overdose of iron tablets in adults Iron poisoning is complicated to treat because by the time someone is symptomatic, much of the iron has already moved out of the blood and into cells, so standard blood tests can look misleadingly normal.
Nasal Decongestants
Topical nasal decongestant sprays containing oxymetazoline or similar compounds are generally safe at labeled doses, but misuse can cause systemic effects. Animal studies have demonstrated that oxymetazoline, even when applied locally, can cause significant ischemic changes, congestion, and tissue necrosis in distant organs.19PubMed Central. Systemic side effects of locally used oxymetazoline In humans, overuse of decongestant sprays most commonly leads to rebound congestion, a worsening cycle that tempts people to use more and more. But in vulnerable individuals, especially young children and people with cardiovascular disease, systemic absorption of these potent vasoconstrictors can raise blood pressure and heart rate to dangerous levels. Oral decongestants like pseudoephedrine carry similar cardiovascular risks in overdose, including dangerously high blood pressure, heart palpitations, and stroke.
Melatonin and Children
Melatonin occupies an unusual category. It is sold as a dietary supplement, not technically a drug in the United States, so it doesn’t carry the same packaging or dosing regulations as OTC medications. Melatonin has become the leading substance involved in unsupervised medication ingestions among children under five in U.S. emergency departments, with the frequency of these incidents increasing fivefold between 2009 and 2021.20JAMA Network Open. Melatonin Use in Young Children: A Systematic Review Most of these ingestions, about 97%, result in minor effects like drowsiness. But some lead to more serious outcomes, and fatalities have been reported.20JAMA Network Open. Melatonin Use in Young Children: A Systematic Review Melatonin gummies, which look and taste like candy, are a particular concern because young children can easily eat a handful.
Why Children and Older Adults Face Extra Risk
Young children are vulnerable for straightforward reasons: they weigh less, so a given dose hits them harder, and they explore the world by putting things in their mouths. Research consistently shows that in the vast majority of unintentional childhood poisonings, unsupervised children ingested medication that was left within their reach.21PubMed Central. Characteristics of unintentional ingestion of oral non-steroidal anti-inflammatory drugs and analgesics in preschool children Child-resistant packaging has prevented hundreds of thousands of accidental ingestions since the 1970s, reducing the rate substantially.22Pediatrics. An Evaluation of the Poison Prevention Packaging Act But these caps only work when adults fully re-secure them after every use, and that often doesn’t happen.23PubMed Central. Ingestion of Over-the-Counter Liquid Medications Emergency Department Visits by Children Aged Less Than 6 Years, 2012-2015 Liquid formulations add another hazard: tenfold dosing errors have been documented with concentrated syrups when parents confuse milliliters with other units or misread graduated droppers.24PubMed. Overdose in young children treated with anti-reflux medications: Poisons enquiry evidence of excess 10-fold dosing errors with ranitidine
Older adults face a different set of vulnerabilities. Age-related changes in kidney and liver function mean drugs are cleared more slowly, so even a standard dose may effectively become an overdose over time. The volume of distribution for fat-soluble drugs increases with age, extending how long those drugs stay active in the body.25PubMed Central. Over the Counter Pain Medications Used by Adults: A Need for Pharmacist Intervention For NSAIDs specifically, older adults have a well-established higher risk of gastrointestinal bleeding and kidney damage compared with younger people taking the same drugs at the same doses.26PubMed Central. Adverse Effects of Analgesics Commonly Used by Older Adults with Osteoarthritis: Focus on Non-Opioid and Opioid Analgesics When you add polypharmacy to the picture, where an older person is taking multiple medications that may interact, the risk compounds quickly.
The Accidental Versus Intentional Divide
People sometimes assume OTC overdoses are always deliberate self-harm, but the reality is more varied. The Northern Ireland emergency department study found that the majority of OTC overdoses were intentional, yet a meaningful subset were accidental.1PubMed. Prevalence of over-the-counter drug-related overdoses at Accident and Emergency departments in Northern Ireland–a retrospective evaluation Accidental overdoses happen through several pathways: double-dipping with combination products (as with acetaminophen), dosing errors with liquid formulations, chronic overuse of laxatives or antacids, and simply taking a medication for longer or in higher amounts than the label recommends because the first dose didn’t seem to work fast enough.
The common thread across accidental overdoses is a mismatch between perceived safety and actual risk. People often think of OTC medications as fundamentally benign because no prescription was required to buy them. This perception gap is real and measurable: research has examined how health literacy and risk perception influence the way adults select and use OTC products, with lower health literacy linked to lower awareness of the potential for harm.27PubMed Central. 3583 Impact of Health Literacy and Risk perception on Over-the-Counter Medication Misuse Labels exist, but reading them carefully before every dose is something many people stop doing after the first use.
Practical Ways to Reduce Risk
The single most important habit is checking the active ingredient list on every OTC product you use, especially when you’re taking more than one. If two products share an active ingredient, you’re doubling up. This applies to combination cold and flu remedies above all else: many contain acetaminophen, an antihistamine, a decongestant, and a cough suppressant in a single product, and people routinely take them alongside standalone versions of those same drugs.
Other steps that meaningfully reduce risk:
- Stick to the label dose: The labeled dose accounts for typical body weight and organ function. Taking more doesn’t usually make the drug work faster; it just increases the chance of toxicity.
- Watch the clock: Minimum dosing intervals exist for a reason. Setting a timer or writing down when you took the last dose prevents accidental re-dosing, especially with round-the-clock medications.
- Store medications out of children’s reach: High shelves or locked cabinets, not countertops or bedside tables. Re-secure child-resistant caps fully every time.
- Ask a pharmacist about interactions: Pharmacists are trained to spot dangerous combinations, and the consultation is free. This is especially important if you’re already taking prescription medications.
On the treatment side, hospitals handle OTC overdoses primarily with supportive care and, where available, specific antidotes. Acetylcysteine for acetaminophen is the best-known example. For many other OTC drugs, there is no targeted antidote, and treatment focuses on decontamination, managing symptoms, and supporting organ function until the drug clears.28European Journal of Pharmaceutics and Biopharmaceutics. Existing and emerging mitigation strategies for the prevention of accidental overdose from oral pharmaceutical products Prevention is always better than treatment, particularly for drugs like loperamide and iron where the damage can progress rapidly and irreversibly.
Products People Rarely Think Of as Dangerous
Beyond the categories covered above, a few OTC products catch people especially off guard. Eye drops containing tetrahydrozoline (the active ingredient in products marketed to reduce redness) have caused serious poisoning when swallowed, particularly in children. Oral ingestion can lead to dangerously low heart rate, low blood pressure, and depressed breathing. Topical pain patches and creams containing menthol, camphor, or methyl salicylate, as discussed earlier with salicylates, can cause systemic toxicity when applied in excess, especially on broken or inflamed skin. Even activated charcoal, sold as a “detox” supplement, can cause aspiration pneumonia if used improperly.
Nasal spray bottles of oxymetazoline deserve a mention in this context as well. While an adult accidentally squirting an extra spray or two is unlikely to cause harm, a toddler who gets hold of a nasal spray bottle and drinks from it can develop significant cardiovascular depression. The small volume of liquid in those bottles is concentrated enough to pose a real threat to a small child. These products don’t carry the same mental weight as a bottle of pills, and that mismatch is exactly what makes them dangerous.