10 Scariest Prescription Drug Side Effects


The following is a list of 10 harmful and potentially deadly side effects of commonly prescribed medications.

Adverse drug reactions are unwanted side effects that have considerable clinical and economic costs, as they can lead to increased emergency department visits and prolonged hospital stays.1

Each year, an estimated 4.5 million Americans visit a physician’s office or emergency room because of side effects related to their prescription medications. Although it may be hard to pinpoint a reaction to one specific medication, the FDA requires drug manufacturers to list all side effects that have been reported in clinical studies in their product’s labeling.

The following is a list of 10 harmful and potentially deadly side effects of commonly prescribed medications.

1. Hallucinations

Hallucinations occur when sensing something that is not really present. Types of hallucinations include visual, auditory, olfactory, tactile, gustatory, and general somatic.

Hallucinations are a common symptom of schizophrenia, but they can also be caused by excessive alcohol intake, drug abuse, depression, sleep deprivation, dementia, or certain prescription medications.2

A number of psychiatric medications such as olanzapine (Zyprexa), quetiapine (Seroquel), and haloperidol (Haldol) have all been associated with causing hallucinations, in addition to zolpidem (Ambien), eszopiclone (Lunesta), clonazepam (Klonopin), lorazepam (Ativan), ropinirole (Requip), and some seizure medications.3

Finally, cephalosporins and sulfa drugs, which are 2 common classes of antibiotics, have been associated with causing hallucinations in rare cases.

2. Memory Loss

Although memory loss is a natural part of getting older, it may also be a side effect of certain medications.

The most notable medication class that can result in memory loss is the nonbenzodiazepine sedative hyponotics, which include Ambien, Lunesta, and Sonata. These medications can sometimes cause amnesia and trigger potentially dangerous behaviors, such as cooking a meal, having sex, or driving a car with no recollection of the event upon awakening.

Other medications that may result in memory loss include benzodiazepines, statins, certain seizure medications, opioids, and incontinence drugs.

3. Priapism

Priapism is an unwanted, painful, persistent erection that is not caused by sexual stimulation or arousal. If left untreated, tissue damage can occur, resulting in the inability to get or maintain an erection.

Causes of priapism include certain medical conditions, trauma, alcohol use, and prescription medications. Medications reported to cause priapism include trazodone (Desyrel), clozapine (Clozaril), hydroxyzine (Atarax), chlorpromazine (Thorazine), prazosin (Minipress), warfarin (Coumadin), testosterone therapy, and serotonin reuptake inhibitors such as sertraline (Zoloft), fluoxetine (Prozac), and paroxetine (Paxil).4

4. Blood Clots

Blood clots form in the body under many normal circumstances in response to injury. However, some prescription medications have been associated with blood clot formation. If left untreated, blood clots can break away from their original source and travel to other parts of the body, which can sometimes be fatal.

Female oral contraceptives and hormone therapy drugs all carry an increased risk for blood clot formation. Additionally, all testosterone replacement products share the same risk for blood clots.

5. Compulsive Behaviors

Compulsive behavior involves repeatedly performing an act without control, which interferes with an individual’s life.

Requip and pramipexole (Mirapex), which are dopamine agonists indicated for Parkinson’s disease and restless legs syndrome, can cause problems with impulse control or compulsive behaviors.

According to the drugs’ package inserts, “case reports suggest that patients can experience intense urges to gamble, increased sexual urges, intense urges to spend money, binge or compulsive eating, and/or other intense urges, and the inability to control these urges.”3

Carbidopa-levodopa (Sinemet) shares this same warning.

More recently, the antipsychotic aripiprazole (Abilify) has been linked with compulsive behavior side effects such as compulsive gambling in some patients.

6. Stevens-Johnson Syndrome

Stevens-Johnson syndrome (SJS) is a rare, life-threatening hypersensitivity reaction of the skin and mucous membranes. During SJS, large macules rapidly spread and form together, leading to blistering, necrosis, and shedding of the skin.5

Lamotrigine (Lamictal) has a relatively high incidence of SJS, especially when initiated at high doses, which led the FDA to require a black box warning on its package labeling to inform consumers of this risk. Other medications that may cause SJS include allopurinol (Zyloprim), acetaminophen (Tylenol), ibuprofen (Motrin), naproxen (Aleve), sulfa drugs, penicillin, barbiturates, and other anticonvulsants.6

7. Birth Defects

A birth defect occurs while a baby develops in the mother’s body. An estimated 1 in every 33 babies in the United States is born with a birth defect.7

Thalidomide is one of the oldest and well-known teratogenic medications. In 1954, thousands of women took the medication—which was then promoted as a wonder drug for treating insomnia, coughs, colds, and headaches—resulting in the death of approximately 2000 children and serious birth defects in more than 10,000 children.

Known teratogenic prescription medications include warfarin, divalproex (Depakote), Paxil, topiramate (Topamax), methotrexate (Rheumatrex), angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, nonsteroidal anti-inflammatory drugs, oral contraceptives, statins, and tetracyclines.

Although the risk for birth defects is highest during the first trimester, women should consult their health care providers about the risk and benefits of all medication use during any stage of pregnancy.

8. Cancer

One of the most surprising instances of a medication related to cancer came when tamoxifen (Nolvadex), which is used to treat breast cancer, was found to increase the risk of uterine cancer. In response, the FDA required the manufacturer to add a black box warning to inform consumers of the risk.

The labeling of type 2 diabetes medication pioglitazone (Actos) includes a warning about an increased risk of bladder cancer, which stemmed from data from an observational study.

All glucagon-like peptide-1 receptor agonists have a black box warning concerning the risk for thyroid C-cell tumors that has been seen in rats and mice. Animal studies have also shown metronidazole (Flagyl) to be carcinogenic.

9. Suicidality

This issue stems back to reports in 1990 that Paxil could lead to suicidality in patients.8 Today, all antidepressants have a black box warning in their labeling about the increased risk of suicidal thinking and behavior in children, adolescents, and young adults with major depressive disorder and other psychiatric disorders.

Current clinical evidence on the topic is inconclusive. Some studies have shown that the use of antidepressants correlates with increased risk of suicidal actions, while other studies have not demonstrated any increased risk.

Other medications that may be associated with suicidal thinking and behavior include montelukast (Singulair), isotretinoin (Claravis), varenicline (Chantix), and mefloquine (Lariam).

10. Death

Sudden cardiac death is the largest cause of natural death in the United States, with an estimated 325,000 adult deaths annually.

A number of antipsychotics such as Seroquel, Zyprexa, and risperidone (Risperdal) have been associated with sudden cardiac death, with increased incidence seen in the elderly and those taking other cardiac medications in combination.9

Antiarrhythmic agents that list sudden cardiac death within their package inserts include sotalol (Betapace), amiodarone (Cordarone), and procainamide (Procanbid). Lastly, the labeling for morphine and Adderall includes warnings about increased risk of sudden death due to cardiac abnormalities.9


  • Sultana J, Cutroneo P, Trifirò G. Clinical and economic burden of adverse drug reactions. J Pharmacol Pharmacother. 2013 Dec; 4(Suppl1): S73—S77. doi: 10.4103/0976-500X.120957.
  • Wade M. Medication-related visual hallucinations: what you need to know. EyeNet Magazine-American Academy of Ophthalmology. March 2015. Accessed January 30, 2016.
  • Requip [package insert]. Research Triangle Park, NC: GlaxoSmithKline; 2014.
  • Drugs reported to cause priapism. UCSF Medical Center. Accessed January 30, 2016.
  • Rehmus W. Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). Merck Manual. Accessed January 28, 2016.
  • List of medications associated with Stevens-Johnson syndrome and toxic epidemal necrolysis. Steven Johnson Syndrome Foundation. Accessed January 28, 2016.
  • Birth Defects. Medline Plus: U.S. National Library of Medicine. Accessed January 28, 2016.
  • Thomas KH, Martin RM, Potokar J, et al. Reporting of drug-induced depression and fatal and non-fatal suicidal behaviour in the UK from 1998 to 2011. BMC Pharmacol Toxicol. 2014 Sep 30;15:54. doi: 10.1186/2050-6511-15-54.
  • Sicouri S, Antzelevitch C. Sudden cardiac death secondary to antidepressant and antipsychotic drugs. Expert Opin Drug Saf. 2008 Mar; 7(2): 181—194. doi: 10.1517/14740338.7.2.181.

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