Antihypertensive drugs lower blood pressure through several distinct mechanisms, and the choice of agent often depends on patient comorbidities. ACE inhibitors such as lisinopril, enalapril, and ramipril block the conversion of angiotensin I to angiotensin II, reducing vasoconstriction and aldosterone secretion, with characteristic side effects of dry cough, hyperkalemia, and rare angioedema. Angiotensin receptor blockers such as losartan, valsartan, and candesartan block the angiotensin II type 1 receptor and provide similar benefits without the dry cough, making them useful alternatives when ACE inhibitors are not tolerated. Beta-blockers such as metoprolol, atenolol, and propranolol block beta-adrenergic receptors, with beta-1 blockade reducing heart rate, contractility, and cardiac output, and beta-2 blockade risking bronchoconstriction, so they are used in hypertension, heart failure, arrhythmias, and angina. Calcium channel blockers block L-type calcium channels in vascular smooth muscle and cardiac cells; dihydropyridines such as amlodipine and nifedipine act mainly as vasodilators, while non-dihydropyridines such as verapamil and diltiazem also slow heart rate and reduce contractility. Thiazide diuretics such as hydrochlorothiazide and chlorthalidone inhibit the sodium-chloride cotransporter in the distal convoluted tubule, promoting sodium and water excretion and reducing blood volume, with the side effects of hypokalemia, hyperuricemia, and hyperglycemia. Diuretics in general increase urine output by promoting sodium and water excretion, and include the more potent loop diuretics such as furosemide, the milder thiazides, and potassium-sparing agents such as spironolactone, which acts as an aldosterone antagonist.
Statins such as atorvastatin, rosuvastatin, and simvastatin inhibit HMG-CoA reductase, the rate-limiting enzyme in cholesterol synthesis, lowering LDL cholesterol by 30 to 50 percent and additionally stabilizing atherosclerotic plaques and reducing inflammation, with myalgia and rare rhabdomyolysis as side effects. Anticoagulants prevent clot formation by interfering with the coagulation cascade and include warfarin, which inhibits vitamin K epoxide reductase and requires monitoring of the INR with a target of 2.0 to 3.0; heparin, which activates antithrombin III; and the direct oral anticoagulants (DOACs) such as rivaroxaban and apixaban, which directly inhibit factor Xa or thrombin. Proton pump inhibitors such as omeprazole, esomeprazole, and pantoprazole irreversibly inhibit the hydrogen-potassium ATPase proton pump in gastric parietal cells, reducing acid production by up to 90 percent and being used for gastroesophageal reflux disease, peptic ulcers, and Helicobacter pylori eradication, although long-term use carries risks of bone fractures and vitamin B12 deficiency.
Several important drug classes target the central nervous system. SSRIs such as fluoxetine, sertraline, and escitalopram block serotonin reuptake in the synapse, increasing serotonin availability, and are first-line treatment for depression and anxiety, although full effect takes four to six weeks and side effects include sexual dysfunction, gastrointestinal upset, and insomnia. SNRIs such as venlafaxine additionally inhibit norepinephrine reuptake, while older tricyclic antidepressants such as amitriptyline and MAO inhibitors such as phenelzine are used less often because of more side effects and dietary restrictions; atypical agents such as bupropion and mirtazapine offer alternative mechanisms. Benzodiazepines such as diazepam, lorazepam, and alprazolam enhance GABA-A receptor activity, increasing chloride influx and neuronal inhibition, and are used for anxiety, insomnia, seizures, and muscle spasms, with risks of sedation, tolerance, dependence, and respiratory depression especially when combined with opioids. Antipsychotics treat schizophrenia and other psychotic disorders; first-generation or typical agents such as haloperidol block dopamine D2 receptors and carry a high risk of extrapyramidal side effects, while second-generation or atypical agents such as risperidone, olanzapine, and quetiapine additionally block serotonin 5-HT2A receptors and have fewer movement side effects but greater metabolic risks. Antiepileptic drugs such as phenytoin, carbamazepine, valproic acid, and levetiracetam prevent seizures by modulating ion channels, enhancing GABA activity, or reducing glutamate activity, and many have narrow therapeutic indices that require monitoring. Corticosteroids such as prednisone, dexamethasone, and hydrocortisone are synthetic analogs of cortisol with potent anti-inflammatory and immunosuppressive effects, acting by inhibiting phospholipase A2 and NF-κB, and are used in asthma, autoimmune disease, and allergies, although long-term use risks osteoporosis, diabetes, and adrenal suppression. In respiratory and allergic disease, antihistamines block histamine H1 receptors, with first-generation agents such as diphenhydramine crossing the blood-brain barrier and causing drowsiness while second-generation agents such as cetirizine and loratadine do not; bronchodilators relax airway smooth muscle, including short-acting beta-2 agonists such as albuterol for rescue, long-acting beta-2 agonists such as salmeterol for maintenance, and anticholinergics such as ipratropium. In diabetes, metformin is the first-line oral agent for type 2 diabetes, reducing hepatic glucose production and increasing insulin sensitivity without causing hypoglycemia when used alone, while injectable insulin preparations are classified by onset and duration into rapid-acting (lispro), short-acting (regular), intermediate (NPH), and long-acting (glargine) forms. Finally, antiemetics such as ondansetron (a 5-HT3 antagonist), metoclopramide (a D2 antagonist and prokinetic), aprepitant (an NK1 antagonist), meclizine (an antihistamine for motion sickness), and dronabinol (a cannabinoid) prevent nausea and vomiting through different mechanisms, and laxatives for constipation include bulk-forming agents such as psyllium, osmotic agents such as lactulose and polyethylene glycol, stimulants such as bisacodyl and senna, and stool softeners such as docusate.