5.3 Common Drugs

Overview

Common drugs on the USMLE are those that appear repeatedly in questions because they treat high-yield diseases, illustrate classic mechanisms, or cause memorable side effects. At this beginner level, the goal is not to memorize every detail, but to recognize the drugs that you must know by name, understand their major clinical uses, and connect each with a small set of “classic” associations.

In this chapter the focus is on what makes these medications “common” for exam purposes. Detailed pharmacology, such as receptor subtypes or complex kinetics, belongs to the Pharmacology section and is not repeated here. Instead, you will see concise connections between drug names, their main indications, and their hallmark adverse effects or contraindications.

Cardiovascular Drugs You Must Recognize

Several cardiovascular medications are particularly high yield because they appear in numerous vignettes about acute coronary syndromes, hypertension, heart failure, and arrhythmias.

Angiotensin converting enzyme inhibitors like lisinopril and enalapril are classic first line drugs for hypertension, especially in patients with diabetes or chronic kidney disease. On exams they are linked with protection of the kidney in diabetic nephropathy and with adverse effects such as dry cough and angioedema. An important test association is their contraindication in pregnancy and bilateral renal artery stenosis.

Angiotensin receptor blockers such as losartan and valsartan share similar indications and are often substituted when the ACE inhibitor cough becomes intolerable. They are also associated with hyperkalemia and are contraindicated in pregnancy, but do not cause bradykinin mediated cough.

Beta blockers that appear constantly are metoprolol, propranolol, atenolol, and carvedilol. You should associate them with chronic management after myocardial infarction, rate control in atrial fibrillation, treatment of chronic heart failure, and reduction of symptoms in hyperthyroidism. Exam questions often test their contraindications in acute decompensated heart failure, bradycardia, and uncontrolled asthma.

Calcium channel blockers divide into dihydropyridines like amlodipine and nifedipine, used mainly for hypertension and vasospasm, and non dihydropyridines like verapamil and diltiazem, which are common in arrhythmia questions due to their rate controlling effects at the atrioventricular node. Constipation with verapamil and gingival hyperplasia with some calcium channel blockers are frequently tested.

Nitrates, especially nitroglycerin and isosorbide dinitrate, are linked with rapid relief of angina. The classic side effects to remember are headache, flushing, and hypotension. The USMLE repeatedly tests the dangerous interaction with phosphodiesterase 5 inhibitors like sildenafil, which can cause severe hypotension.

Common antiarrhythmics include amiodarone and digoxin. Amiodarone is associated with many organ toxicities such as thyroid dysfunction, pulmonary fibrosis, and corneal deposits. Digoxin is tied to symptoms of toxicity like nausea, vomiting, vision changes, and arrhythmias, especially in the setting of hypokalemia or drug interactions.

Common cardiovascular drugs and their key words are summarized below.

Common Antibiotics and Antimicrobials

Antimicrobial drugs are among the most frequently tested medications, because they connect microbiology and pharmacology with clinical decision making. The details of spectrum and mechanisms are discussed in the Antibiotics and Antimicrobials sections, so here the focus is on the drugs that appear again and again in typical question stems.

Penicillins, especially penicillin G and penicillin V, are classic for gram positive organisms and syphilis. Amoxicillin and ampicillin are frequently mentioned for otitis media, sinusitis, and empiric coverage of common community infections. An important association is allergic reactions, including anaphylaxis, and cross reactivity with certain cephalosporins.

Cephalosporins such as cefazolin, ceftriaxone, and ceftazidime are common in surgical prophylaxis and treatment of meningitis or serious gram negative infections. Ceftriaxone is strongly associated with meningitis and gonorrhea treatment. Exam questions often test the disulfiram like reaction with some cephalosporins when combined with alcohol.

Vancomycin is a key drug for methicillin resistant Staphylococcus aureus and severe Clostridioides difficile colitis when given orally. It is associated with nephrotoxicity, ototoxicity, and the classic “red man syndrome” infusion reaction that occurs if the drug is given too quickly.

Macrolides, especially azithromycin, clarithromycin, and erythromycin, are linked with atypical pneumonia and sexually transmitted infections like chlamydia. Common test associations include QT prolongation and inhibition of cytochrome P450 for some agents.

Fluoroquinolones like ciprofloxacin and levofloxacin appear in urogenital and gastrointestinal infection questions. Exams highlight their risk for tendon rupture, especially in older patients or those on steroids, and their contraindication in pregnancy and growing children due to cartilage damage.

Trimethoprim sulfamethoxazole, often abbreviated TMP SMX, is high yield for urinary tract infections, Pneumocystis jirovecii pneumonia prophylaxis and treatment, and certain skin infections caused by community acquired MRSA. It is associated with hyperkalemia, bone marrow suppression, and sulfa allergies.

Metronidazole is heavily tested for anaerobic infections and infections with protozoa like Giardia and Trichomonas. It is strongly associated with a disulfiram like reaction when combined with alcohol.

Endocrine and Metabolic Drugs

Endocrine drugs are common on the USMLE because they mirror very frequent clinical problems such as diabetes, thyroid disease, and adrenal disorders.

Insulins are central in diabetes questions. Rapid acting agents like lispro, aspart, and glulisine are connected with mealtime glucose control. Long acting insulins such as glargine and detemir provide basal control. The chief risk to recognize is hypoglycemia, especially when meals are skipped or with excessive dosing.

Metformin is a foundational oral drug for type 2 diabetes. The test often emphasizes that it decreases hepatic gluconeogenesis, is weight neutral or causes weight loss, and is contraindicated in severe kidney disease because of the risk of lactic acidosis. You should associate it with gastrointestinal side effects like diarrhea but not with hypoglycemia when used alone.

Sulfonylureas such as glyburide and glipizide are associated with increased insulin release and a significant risk of hypoglycemia, particularly in elderly patients. Weight gain is also common.

SGLT2 inhibitors such as canagliflozin and empagliflozin appear in questions that combine diabetes with cardiovascular disease or kidney disease. They are associated with glucosuria, an increased risk of urinary tract and genital infections, and volume depletion. The exams also connect them with some cardiovascular and renal protective effects.

For thyroid disease, levothyroxine is the synthetic T4 most commonly used for hypothyroidism and myxedema. Excess replacement can cause symptoms of hyperthyroidism like palpitations and weight loss. For hyperthyroidism, thioamides such as methimazole and propylthiouracil are common. Methimazole is avoided in the first trimester of pregnancy, and both drugs are associated with agranulocytosis, which on exams presents as fever and sore throat in a patient on antithyroid medication.

Glucocorticoids such as prednisone, hydrocortisone, and dexamethasone are common across many organ system questions. They are used for inflammation, autoimmune diseases, and adrenal insufficiency. On exams they are tied to chronic side effects like osteoporosis, hyperglycemia, immunosuppression, and adrenal suppression. Sudden withdrawal after chronic therapy is a classic cause of adrenal crisis.

Central Nervous System Drugs

CNS drugs show up frequently in neurology and psychiatry questions, but also in general medicine vignettes involving pain, seizures, or anesthesia.

For depression, the selective serotonin reuptake inhibitors such as fluoxetine, sertraline, and citalopram are foundational. The test links them with delayed onset of therapeutic effect, sexual dysfunction, and the risk of serotonin syndrome when combined with other serotonergic drugs. Serotonin syndrome features mental status changes, autonomic instability, and neuromuscular abnormalities like clonus.

Tricyclic antidepressants like amitriptyline appear less commonly in practice but are very testable due to their adverse effects. They are associated with anticholinergic symptoms, sedation, and cardiac toxicity such as arrhythmias and wide QRS on overdose. Nortriptyline is sometimes highlighted as a TCA used for neuropathic pain.

For psychosis and schizophrenia, typical antipsychotics like haloperidol and atypicals like risperidone, olanzapine, and clozapine are highly testable. Extrapyramidal symptoms, tardive dyskinesia, and neuroleptic malignant syndrome are classic associations for high potency typical antipsychotics. Atypicals have prominent metabolic side effects like weight gain and dyslipidemia. Clozapine is uniquely associated with agranulocytosis and requires regular blood count monitoring.

Benzodiazepines such as diazepam, lorazepam, and midazolam are central in acute seizure and anxiety questions, as well as procedural sedation. They are known for sedation, respiratory depression, and dependence. Flumazenil is the antagonist used in overdose or reversal cases.

Common antiepileptic drugs like phenytoin, valproic acid, carbamazepine, and lamotrigine appear repeatedly. Phenytoin is linked with gingival hyperplasia, hirsutism, and ataxia. Valproic acid is associated with neural tube defects in pregnancy and hepatotoxicity. Carbamazepine commonly causes bone marrow suppression and is a drug of choice for trigeminal neuralgia. Lamotrigine is high yield for its risk of Stevens Johnson syndrome, especially with rapid dose escalation.

For pain, opioids such as morphine, oxycodone, hydromorphone, and codeine are constant in exam questions. The classic triad in overdose is respiratory depression, miosis, and coma, and naloxone is the reversal agent. Constipation and dependence are major chronic side effects. Nonsteroidal anti inflammatory drugs such as ibuprofen and naproxen are commonly associated with peptic ulcer disease, kidney injury, and inhibition of platelet function. Aspirin is unique for its irreversible platelet effect and salicylate toxicity.

Respiratory and Allergy Medications

Respiratory drugs are frequently tested in asthma and chronic obstructive pulmonary disease scenarios, and in allergy related questions.

Short acting beta agonists such as albuterol provide rapid relief of acute asthma symptoms. Long acting beta agonists like salmeterol and formoterol are used for maintenance therapy but must be combined with inhaled corticosteroids to reduce the risk of asthma related death. Beta agonists are associated with tremor and tachycardia due to systemic sympathetic effects.

Inhaled corticosteroids such as fluticasone and budesonide are first line for long term control of persistent asthma. Classic associations are oral candidiasis and hoarseness, which can be minimized by rinsing the mouth after use. Systemic steroids, like prednisone, are reserved for acute exacerbations and severe disease.

Leukotriene receptor antagonists such as montelukast and zafirlukast appear in vignettes about aspirin induced asthma or exercise induced bronchospasm. They are administered orally and associated with rare neuropsychiatric side effects in some reports.

For allergic rhinitis and urticaria, antihistamines are common. First generation H1 blockers like diphenhydramine and chlorpheniramine often cause sedation and anticholinergic effects, which are more pronounced than with second generation agents. Second generation H1 blockers like loratadine and cetirizine are less sedating and frequently used for chronic allergies.

Anticholinergic bronchodilators such as ipratropium and tiotropium are used in chronic obstructive pulmonary disease and sometimes in asthma. Their hallmark side effects are dry mouth and sometimes urinary retention.

Gastrointestinal and Hepatic Drugs

Gastrointestinal drugs are often tested through common complaints like acid reflux, ulcers, nausea, diarrhea, and constipation.

Proton pump inhibitors such as omeprazole and pantoprazole are central to treatment of gastroesophageal reflux disease and peptic ulcer disease, especially when Helicobacter pylori is present. Long term use is associated with increased risk of Clostridioides difficile infection, decreased magnesium, and possible increased fracture risk.

H2 receptor blockers like ranitidine and famotidine are less potent acid suppressors used for milder symptoms. They are linked with rare side effects such as confusion in elderly patients.

Antiemetics like ondansetron are prominent in chemotherapy and post operative nausea questions. Ondansetron is a serotonin receptor antagonist associated with QT prolongation and constipation.

Laxatives are often grouped together, but commonly tested examples include osmotic agents like lactulose, which is also used in hepatic encephalopathy by promoting ammonia excretion, and polyethylene glycol. Overuse of stimulant laxatives can lead to dependence and electrolyte disturbances.

Antidiarrheal drugs such as loperamide work on opioid receptors in the gut and are associated with constipation. In infectious diarrhea, especially with systemic signs, antimotility agents are usually avoided.

Drugs for inflammatory bowel disease, such as mesalamine and biologics like infliximab, appear in vignettes about chronic diarrhea and weight loss. Infliximab is associated with reactivation of latent tuberculosis, which makes TB screening a classic step before therapy.

Reproductive and Obstetric Drugs

Reproductive system drugs are very testable because many questions involve pregnancy safety, contraception, or hormone related conditions.

Combined oral contraceptive pills containing estrogen and progestin are associated with prevention of pregnancy, regulation of menstrual cycles, and improvement of dysmenorrhea. On exams they are contraindicated in women who smoke heavily and are older than 35, those with a history of thromboembolism, and certain types of migraine. They can increase the risk of venous thromboembolism and mild blood pressure elevations.

Progestin only preparations such as the mini pill or depo medroxyprogesterone injections are options for women who cannot take estrogen. They are often associated with irregular bleeding and delayed return to fertility after injections.

Selective estrogen receptor modulators include tamoxifen and raloxifene. Tamoxifen is classically used for estrogen receptor positive breast cancer, with a risk of endometrial carcinoma and venous thromboembolism. Raloxifene is used for osteoporosis in postmenopausal women and does not increase the risk of endometrial cancer.

Drugs used in pregnancy include oxytocin for labor induction, associated with uterine hyperstimulation if used excessively, and tocolytics such as nifedipine and indomethacin to delay preterm labor. Magnesium sulfate is used for seizure prophylaxis in preeclampsia and treatment of eclampsia and can cause decreased deep tendon reflexes and respiratory depression at high levels.

Teratogenic drugs such as isotretinoin, valproic acid, and angiotensin converting enzyme inhibitors are heavily tested. Isotretinoin, in particular, is associated with severe birth defects and requires strict pregnancy prevention measures in women of childbearing age.

Hematologic and Oncologic Drugs

Common hematologic and oncologic medications appear frequently in questions about thrombosis, anemia, and cancer therapy.

Anticoagulants such as heparin and warfarin are central. Unfractionated heparin is associated with rapid onset anticoagulation, partial thromboplastin time monitoring, and the risk of heparin induced thrombocytopenia. Low molecular weight heparins like enoxaparin are used more commonly in practice and have more predictable pharmacokinetics.

Warfarin inhibits vitamin K dependent clotting factors and is monitored with the international normalized ratio. It carries a risk of bleeding and is affected by many drug interactions. Warfarin is teratogenic and is often replaced with heparin during pregnancy. On exams, vitamin K and fresh frozen plasma or prothrombin complex concentrate are used in significant bleeding.

Direct oral anticoagulants such as apixaban and rivaroxaban are increasingly common. They do not require routine monitoring and are associated with bleeding risk. Specific reversal agents are tested, for example idarucizumab for dabigatran.

Antiplatelet drugs include aspirin and clopidogrel. Aspirin irreversibly inhibits cyclooxygenase and is central in secondary prevention of cardiovascular events. It is associated with Reye syndrome in children and salicylate toxicity. Clopidogrel is an ADP receptor blocker frequently used after stent placement, with bleeding and rare thrombotic thrombocytopenic purpura as associations.

In oncology, many chemotherapeutic drugs are high yield for their characteristic toxicities. Doxorubicin is linked with cardiomyopathy, which can be prevented or reduced with dexrazoxane. Cyclophosphamide is associated with hemorrhagic cystitis, which can be mitigated with mesna. Cisplatin is known for nephrotoxicity and ototoxicity. Vincristine is associated with peripheral neuropathy, while vinblastine is more myelosuppressive.

Anti inflammatory and Immunologic Drugs

Anti inflammatory and immunomodulating agents are common in rheumatology, dermatology, and transplant questions.

Nonsteroidal anti inflammatory drugs like ibuprofen, naproxen, indomethacin, and ketorolac inhibit cyclooxygenase enzymes and reduce prostaglandin synthesis. They are associated with gastrointestinal ulcers, renal impairment, and exacerbation of hypertension. Selective COX 2 inhibitors such as celecoxib have less gastrointestinal risk but may increase cardiovascular risk.

Disease modifying antirheumatic drugs include methotrexate, sulfasalazine, hydroxychloroquine, and biologic agents like tumor necrosis factor alpha inhibitors. Methotrexate is a cornerstone in rheumatoid arthritis and is associated with hepatotoxicity, bone marrow suppression, and folate deficiency. Folic acid supplementation is often used to reduce toxicity.

Tumor necrosis factor alpha inhibitors such as infliximab, adalimumab, and etanercept are strongly associated with increased risk of serious infections, particularly reactivation of latent tuberculosis and fungal infections. Screening for tuberculosis is a standard step before starting therapy in USMLE questions.

Calcineurin inhibitors such as cyclosporine and tacrolimus are used to prevent organ transplant rejection. They are associated with nephrotoxicity and hypertension. Gingival hyperplasia and hirsutism are more common with cyclosporine.

Infectious Disease and Antiviral Drugs

Antiviral and antifungal agents are high yield due to their association with common infections like influenza, herpes, HIV, and fungal diseases.

For herpesviruses, acyclovir, valacyclovir, and famciclovir are common. They are used for herpes simplex virus and varicella zoster virus infections. Nephrotoxicity due to crystallization in renal tubules can occur, especially if not adequately hydrated.

Antiretroviral drugs for HIV are numerous, but some names recur frequently, such as zidovudine, tenofovir, efavirenz, and protease inhibitors like ritonavir. Zidovudine is linked with bone marrow suppression and is used in prevention of maternal to child transmission. Tenofovir is associated with kidney injury and bone density loss. Protease inhibitors often cause metabolic syndrome and lipodystrophy.

For influenza, neuraminidase inhibitors such as oseltamivir and zanamivir are used for early treatment or prophylaxis and are most effective when started within 48 hours of symptom onset.

Common antifungal agents include azoles like fluconazole and voriconazole, associated with inhibition of cytochrome P450 and hepatotoxicity, and amphotericin B, which is notorious for nephrotoxicity and infusion related reactions like chills and fever. Nystatin is often used topically for candidiasis.

Key Patterns and Exam Strategy

The USMLE often tests drugs by describing the clinical scenario and asking you to identify the most appropriate medication or its major adverse effect. For common drugs, pattern recognition is extremely important.

Certain combinations of disease and drug are almost stereotyped. A patient with newly diagnosed type 2 diabetes and obesity is linked to starting metformin. A patient with systolic heart failure is associated with an ACE inhibitor, beta blocker, and sometimes spironolactone. A postoperative venous thromboembolism is associated with heparin followed by warfarin.

Adverse effect questions are especially common. When a patient on a particular medication presents with a new symptom, you should ask whether that symptom is a classic side effect. Examples include cough in a patient on an ACE inhibitor, gingival hyperplasia with phenytoin or certain calcium channel blockers, and hyperkalemia with ACE inhibitors, ARBs, or potassium sparing diuretics.

Drug interactions and contraindications are also high yield. Recognizing that warfarin is unsafe in pregnancy, that NSAIDs can worsen kidney function, or that clozapine can cause life threatening neutropenia are typical exam level tasks.

By focusing on these widely used and often tested drugs, and by linking each to its primary indication and characteristic risks, you develop a practical foundation that will support deeper study in the dedicated Pharmacology and organ system chapters.