Taking someone else’s prescription medication can cause serious health problems, land you in the emergency room, and is illegal under federal law. Even if the drug seems harmless or you’re taking it for the same symptoms the other person had, a prescription is tailored to one specific person’s body, medical history, and other medications. What works safely for them can be dangerous, or even fatal, for you.
In 2016, an estimated 358,247 emergency department visits in the U.S. resulted from nonmedical use of pharmaceuticals. Of those visits, 23% involved unresponsiveness or cardiorespiratory failure, and 40% led to hospitalization.
Why the Same Drug Affects Two People Differently
When a doctor writes a prescription, the dose is calculated based on your specific body. Your weight, age, kidney function, liver health, and even your genetics all influence how quickly you process a drug and how long it stays in your system. Someone with reduced kidney function, for example, clears many medications more slowly, which means a standard dose can build up to toxic levels in their body. The FDA requires drug manufacturers to study these differences and provide adjusted dosing recommendations for people with impaired kidney function, precisely because a one-size-fits-all dose doesn’t exist.
Body weight matters in ways that aren’t always obvious. In people who are overweight or obese, fat tissue changes how drugs distribute throughout the body, and standard weight-based calculations can overestimate or underestimate the right dose. Age plays a role too: older adults typically metabolize drugs more slowly, while younger adults may process them faster. A pill that’s perfectly calibrated for a 65-year-old woman weighing 130 pounds could overwhelm or undertreat a 25-year-old man weighing 200 pounds.
Dangerous Drug Interactions
The biggest hidden risk of taking someone else’s medication is what it does in combination with drugs you’re already taking. Your doctor and pharmacist track your full medication list specifically to prevent deadly interactions. When you borrow a pill from a friend or family member, nobody is checking for conflicts.
Some combinations are life-threatening. Opioid painkillers, alcohol, antihistamines, and sedatives all slow your breathing. Taking any two of these together increases the risk of respiratory depression, where your breathing becomes so shallow it can stop entirely. People who use benzodiazepines (commonly prescribed for anxiety or sleep) alongside opioids face an especially high risk of overdose and death. Chest wall rigidity from fentanyl exposure has also been identified as a contributing factor in fentanyl-related deaths.
Stimulant medications, like those prescribed for ADHD, create a different kind of danger. Combining a stimulant with common cold medicines that contain decongestants can spike your blood pressure to dangerous levels or trigger irregular heart rhythms. These are interactions most people would never think to worry about.
Antibiotics Carry Their Own Risks
Borrowing leftover antibiotics is one of the most common forms of prescription sharing, and it’s uniquely harmful. Taking an antibiotic that wasn’t prescribed for your specific infection means the type of antibiotic, the dose, and the duration are likely all wrong. This doesn’t just fail to cure you. It actively breeds resistant bacteria in your body.
Research shows that after a course of antibiotics, individual resistance to that drug can persist for up to 12 months. That means the next time you actually need that antibiotic, it may not work, forcing doctors to use stronger second-line drugs with more side effects. On a larger scale, antibiotic resistance leads to more severe infections, longer hospital stays, and higher mortality rates.
Antibiotics also cause a significant share of drug-related emergencies on their own. They account for roughly 20% of all drug-related emergency department visits in the U.S., with adverse effects ranging from gastrointestinal problems to neurological and psychiatric symptoms. Some reactions, like liver damage from certain common antibiotic combinations, can be life-threatening.
Masking Symptoms and Delaying Diagnosis
When you treat your own symptoms with someone else’s medication, you may feel temporarily better while a serious underlying condition goes undetected. Pain medications can mask the warning signs of appendicitis or a heart attack. Anti-inflammatory drugs can quiet the symptoms of an autoimmune disease that needs specific treatment. Borrowing someone’s blood pressure medication when you feel dizzy could drop your pressure to dangerous levels if dizziness wasn’t caused by hypertension in the first place.
Self-medication is associated with worsening of pre-existing conditions, increased risk of drug dependence, and delayed diagnosis of severe diseases. The temporary relief isn’t worth the trade-off of discovering a treatable condition months later, after it’s become harder to manage.
The Legal Consequences Are Real
Most people don’t realize that possessing someone else’s prescription medication is a federal crime under the Controlled Substances Act. This applies even if you had no intention of selling it. Simply having a controlled substance that wasn’t prescribed to you counts as illegal possession.
For a first offense, knowingly possessing any controlled substance carries up to one year in prison, a minimum fine of $1,000, or both. The penalties escalate significantly depending on the type of drug, the amount, and whether there’s any indication you intended to distribute it. Federal penalties for drug offenses range from less than one year to life imprisonment and fines up to $4 million for first offenses at the higher end of the scale. Even an unsuccessful attempt or conspiracy to commit a drug offense is punishable by the same sentence as the completed crime.
The person who shared the medication faces legal risk too. Giving your prescription pills to someone else, even with good intentions, can be classified as distribution of a controlled substance.
High-Risk Drug Categories
While taking any non-prescribed medication carries risk, certain drug classes are especially dangerous:
- Opioid painkillers: These suppress breathing, and without an established tolerance, even a single dose meant for someone else can cause fatal respiratory depression. People with psychiatric disorders or those taking sedatives face the highest risk.
- Sedatives and sleep medications: These also slow breathing and compound dangerously with alcohol, opioids, and antihistamines.
- Stimulants: Borrowing ADHD medication can cause dangerous spikes in heart rate and blood pressure, particularly if you have an undiagnosed heart condition.
- Blood thinners: The wrong dose can cause uncontrolled bleeding or, conversely, fail to prevent a clot.
- Antibiotics: Wrong drug selection promotes resistant bacteria and can cause serious allergic reactions or organ damage.
What to Do With Leftover Medications
If you have unused prescription drugs at home, the safest step is to dispose of them so they’re never available to share. The FDA recommends using a drug take-back program, which you can find at many pharmacies and community centers, or mailing them back using prepaid drug mail-back envelopes.
If neither option is available, mix the pills with something unpleasant like used coffee grounds, dirt, or cat litter. Place the mixture in a sealed container and throw it in your household trash. Scratch off all personal information from the original packaging before discarding it. Fentanyl patches are an exception: even used patches contain enough medication to be dangerous and should be flushed down the toilet, following the instructions on the packaging.