Many consumers assume that medicines sold over the counter are inherently safe. If a product can be picked up in a supermarket aisle or purchased without a prescription at a local pharmacy, it is often perceived as low risk.
But health experts say that assumption can be misleading.
While over-the-counter (OTC) medicines are safe when used correctly, several widely available products can cause dependence, misuse, or serious health complications when taken in higher-than-recommended doses, for longer periods than advised, or for unintended purposes.
Below are five commonly used medicines that experts say deserve closer attention.
1. Codeine-Based Painkillers: Short-Term Relief, Long-Term Risk
Codeine is an opioid used to treat mild to moderate pain and, in some cases, to suppress coughs. In non-prescription products, it is typically combined with ibuprofen or paracetamol.
Once ingested, the body converts codeine into morphine — the compound responsible for its pain-relieving effects.
While effective, codeine carries well-documented risks. Common side effects include drowsiness, constipation, nausea, and dizziness. At higher doses, it can slow breathing, impair coordination, and increase the risk of overdose.
Genetic Vulnerability
Some individuals are “ultra-rapid metabolisers,” meaning their bodies convert codeine into morphine much faster than normal.
This genetic variation, more common in people of North African, Middle Eastern, and Oceanian descent, can lead to dangerously high morphine levels — even when standard doses are taken.
Tolerance and Dependence
With repeated use, the brain’s opioid receptors adapt to codeine. Over time, users may find that the same dose no longer provides relief — a phenomenon known as tolerance. This can lead to escalating doses and, eventually, physical dependence.
Abruptly stopping codeine after prolonged use may trigger withdrawal symptoms such as anxiety, sweating, restlessness, and insomnia.
In the United Kingdom, the Medicines and Healthcare products Regulatory Agency (MHRA) limits OTC pack sizes to 32 tablets and recommends non-prescription codeine be used for no more than three days.
2. Decongestants: When Relief Turns Into Rebound
Decongestants are commonly used to relieve blocked noses during colds or allergies. They are available as oral tablets containing pseudoephedrine and as nasal sprays or drops containing xylometazoline or oxymetazoline.
These medications work by narrowing blood vessels in the nasal passages, reducing swelling and mucus production.
The Rebound Effect
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Overusing nasal sprays can lead to a condition known as rhinitis medicamentosa, or rebound congestion. As the medication loses effectiveness — a process called tachyphylaxis — users may increase their frequency of use, trapping themselves in a cycle of worsening congestion and dependency.
Long-term misuse can damage nasal tissues, causing dryness, nosebleeds, and, in severe cases, perforation of the nasal septum.
Most medical guidance advises limiting nasal decongestant sprays to three to five days.
Pseudoephedrine and Misuse
Pseudoephedrine, while effective, has mild stimulant properties. It appears on the list of substances banned in competition by the World Anti-Doping Agency due to its performance-enhancing potential.
It is also used illicitly in the production of methamphetamine, which led to tighter sales restrictions following regulatory reviews in 2016.
3. Sleeping Tablets: Sedation With Consequences
Sedating antihistamines such as promethazine and diphenhydramine are sold as short-term sleep aids.
Although widely used, recent research has linked sedating antihistamines to rising numbers of deaths, prompting renewed calls for stricter oversight of their supply.
Tolerance and Rebound Insomnia
Promethazine can quickly lead to tolerance, requiring higher doses for the same sedative effect. Long-term users often report severe rebound insomnia when attempting to stop.
The drug has also gained attention in recreational settings. It is sometimes used in “purple drank,” a mixture of cough syrup containing promethazine combined with soft drinks.
This combination can cause extreme sedation, slowed breathing, and potentially life-threatening complications.
4. Cough Syrups: The Hidden Dangers of Dextromethorphan
Dextromethorphan (DXM) is a common cough suppressant found in many OTC syrups and cold remedies.
At recommended doses, it is generally safe and effective. However, a 2021 review identified DXM as the most frequently misused over-the-counter medicine examined in the study.
At high doses, DXM blocks NMDA receptors in the brain, producing dissociative and hallucinogenic effects similar to ketamine. These psychoactive properties have contributed to its misuse, particularly among adolescents and young adults.
Large doses can also cause confusion, agitation, irregular heartbeat, and, in severe cases, life-threatening complications.
5. Laxatives: Myths and Misuse
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Stimulant laxatives are designed to treat short-term constipation by stimulating the muscles of the gut to move stool along.
However, misuse is common among individuals with eating disorders, athletes in weight-restricted sports, and those who mistakenly believe that daily bowel movements are medically necessary.
In reality, constipation is typically defined as fewer than three bowel movements per week.
The Dangerous Myth
Research shows that stimulant laxatives do not prevent calorie absorption, contrary to popular belief. Instead, misuse can lead to dehydration, electrolyte imbalances, and long-term intestinal damage.
Severe electrolyte disturbances can affect heart rhythm and kidney function, posing serious health risks.
In 2020, the MHRA introduced new pack-size limits and strengthened warning labels in response to growing concerns.
Why Over-the-Counter Doesn’t Always Mean Risk-Free
The common thread linking these medicines is not that they are inherently unsafe. When used correctly and for short durations, they can provide effective relief.
However, experts caution that OTC availability can create a false sense of security — particularly when products are purchased online without professional advice.
While regulators have implemented restrictions and warning labels, research suggests misuse remains widespread.
Health professionals say improved awareness, clearer labeling, and better public education are critical to ensuring that these medicines remain helpful tools rather than sources of harm.
Over-the-counter does not always mean harmless — and understanding the risks could prevent avoidable health consequences.
