This list includes 41 Medications that start with O, from “Obeticholic acid (Ocaliva)” to “Ozenoxacin (Xepi).” It covers common prescription drugs, topical antibiotics, and specialty treatments across multiple therapeutic areas.
Medications that start with O are drugs whose generic names begin with O. Some, like oxycodone, have names rooted in historical naming conventions.
Below you’ll find the table with Generic name, Brand name, Drug class, Common uses, and Common side effects.
Generic name: The generic name lists the official nonproprietary drug name, so you can identify the active ingredient quickly.
Brand name: Brand name shows common trade names so you can match a generic to the products you see in pharmacies.
Drug class: Drug class groups medications by how they work, helping you understand therapeutic purpose at a glance.
Common uses: Common uses lists typical conditions treated, so you can quickly see why a medication might be prescribed.
Common side effects: Common side effects highlights frequent, mild adverse effects so you know what to watch for during treatment.
Last updated: September 28, 2025.
Medical disclaimer: This list is informational and does not replace advice from healthcare professionals.
Medications that start with O
| Medication | Drug class | Common uses | Typical adult dose (common form) |
|---|---|---|---|
| Olanzapine (Zyprexa) | Antipsychotic (atypical) | Schizophrenia, bipolar disorder | 5–20 mg PO once daily |
| Olmesartan (medoxomil) | ARB antihypertensive | Hypertension | 20–40 mg PO once daily |
| Olopatadine (Patanol, Pataday) | Antihistamine/mast‑cell stabilizer | Allergic conjunctivitis (and allergic rhinitis formulations) | 1 drop 0.1% each eye twice daily (eye drop) |
| Omeprazole | Proton pump inhibitor | GERD, peptic ulcer disease | 20–40 mg PO once daily |
| Omalizumab (Xolair) | Anti‑IgE monoclonal antibody | Severe allergic asthma, chronic spontaneous urticaria | 150–375 mg SC every 2–4 weeks (weight/IgE based) |
| Ocrelizumab (Ocrevus) | Anti‑CD20 monoclonal antibody | Relapsing and primary progressive multiple sclerosis | 300 mg IV day 1 & 14; then 600 mg IV every 6 months |
| Ondansetron | 5‑HT3 antagonist antiemetic | Nausea/vomiting from chemo, postop | 4–8 mg IV/PO every 8 hours as needed |
| Oseltamivir (Tamiflu) | Neuraminidase inhibitor | Influenza treatment and post‑exposure prophylaxis | 75 mg PO twice daily (treatment) |
| Ofloxacin | Fluoroquinolone antibiotic | Respiratory, urinary, ocular infections | 200–400 mg PO every 12 hours |
| Oxcarbazepine | Antiepileptic | Focal seizures, mood stabilization adjunct | 300 mg PO twice daily (adjust as needed) |
| Oxazepam | Benzodiazepine | Anxiety, alcohol withdrawal, insomnia | 10–30 mg PO 2–4 times daily as needed |
| Oxacillin | Penicillinase‑resistant penicillin antibiotic | MSSA (methicillin‑sensitive Staph) infections | 1–2 g IV every 4–6 hours |
| Oxaliplatin | Platinum chemotherapy agent | Colorectal cancer (in combination regimens) | 85 mg/m2 IV every 2 weeks |
| Oxandrolone | Anabolic steroid | Weight restoration after catabolic states | 2.5–20 mg PO daily divided |
| Oxaprozin | NSAID (nonsteroidal anti‑inflammatory) | Osteoarthritis, rheumatoid arthritis, pain | 600–1,800 mg PO once daily |
| Oxymetazoline | Alpha‑adrenergic topical decongestant | Nasal congestion (topical) and ocular redness | 2–3 sprays each nostril every 12 hours (nasal) |
| Oxymorphone | Opioid analgesic | Moderate–severe pain | 5–10 mg PO every 4–6 hours as needed |
| Oxycodone | Opioid analgesic | Moderate–severe pain | 5–15 mg PO every 4–6 hours as needed |
| Oxybutynin | Antimuscarinic (bladder relaxant) | Overactive bladder, urinary incontinence | 5 mg PO two–three times daily |
| Ozenoxacin (Xepi) | Topical quinolone antibiotic | Impetigo (superficial skin infection) | Apply to affected area twice daily (topical) |
| Oxiconazole | Topical imidazole antifungal | Dermatophyte and yeast skin infections | Apply cream twice daily (topical) |
| Ospemifene (Osphena) | Selective estrogen receptor modulator | Dyspareunia from menopausal vaginal atrophy | 60 mg PO once daily |
| Opicapone | COMT inhibitor | Adjunctive treatment in Parkinson’s disease motor fluctuations | 50 mg PO at bedtime |
| Orlistat | Pancreatic lipase inhibitor | Weight loss in obesity | 120 mg PO three times daily with meals |
| Orphenadrine | Muscle relaxant/anticholinergic | Acute muscle spasm and pain | 100 mg PO twice daily or 120 mg ER once daily |
| Olsalazine | 5‑ASA derivative (anti‑inflammatory) | Ulcerative colitis maintenance | 500 mg–1 g PO twice daily |
| Omadacycline (Nuzyra) | Tetracycline‑class antibiotic | Community‑acquired pneumonia, skin infections | 100 mg IV then 300 mg PO once daily |
| OnabotulinumtoxinA (Botox) | Botulinum toxin type A neurotoxin | Spasticity, chronic migraine, cosmetic lines | 20–200 units IM/SC depending on indication |
| Ocriplasmin (Jetrea) | Proteolytic enzyme (intravitreal) | Symptomatic vitreomacular adhesion | 0.125 mg intravitreal single injection |
| Oxytocin | Uterotonic peptide hormone | Induction/augmentation of labor, postpartum hemorrhage | 10–40 units IV infusion per obstetric protocol |
| Oxytetracycline | Tetracycline antibiotic | Acne, respiratory and urinary infections | 250–500 mg PO every 6–12 hours |
| Osimertinib (Tagrisso) | EGFR tyrosine kinase inhibitor | EGFR‑mutated non‑small cell lung cancer | 80 mg PO once daily |
| Osilodrostat (Isturisa) | Cortisol synthesis inhibitor | Cushing’s disease | 1–4 mg PO twice daily (titrate) |
| Olaparib (Lynparza) | PARP inhibitor | BRCA‑mutated ovarian and breast cancers | 300 mg PO twice daily |
| Octreotide | Somatostatin analogue | Acromegaly, variceal bleeding, carcinoid syndrome | 50–100 mcg SC 2–3 times daily or 20–30 mg IM monthly (LA) |
| Obinutuzumab (Gazyva) | Anti‑CD20 monoclonal antibody | Chronic lymphocytic leukemia, follicular lymphoma | 1,000 mg IV on specific cycle days per protocol |
| Ofatumumab (Arzerra, Kesimpta) | Anti‑CD20 monoclonal antibody | CLL and relapsing multiple sclerosis | 20 mg SC weekly x3 then monthly (MS); IV dosing for CLL |
| Olodaterol | Long‑acting beta2 agonist (inhaled) | COPD maintenance therapy | 5 mcg inhaled once daily via nebulizer/inhaler |
| Omacetaxine mepesuccinate (Synribo) | Protein synthesis inhibitor (chemotherapy) | CML resistant to tyrosine kinase inhibitors | 1.25 mg/m2 SC twice daily for 14 days (cycle 1) |
| Ozanimod (Zeposia) | S1P receptor modulator | Relapsing MS, ulcerative colitis | 0.92 mg PO once daily after titration |
| Obeticholic acid (Ocaliva) | Farnesoid X receptor agonist | Primary biliary cholangitis (PBC) | 5–10 mg PO once daily (adjust with response) |
Descriptions
Olanzapine (Zyprexa)
A commonly used antipsychotic for psychosis and mood stabilization; watch for sedation, weight gain and metabolic changes.
Olmesartan (medoxomil)
An angiotensin receptor blocker for blood pressure; monitor kidney function and potassium; rare sprue‑like enteropathy reported.
Olopatadine (Patanol, Pataday)
Topical antihistamine eye drop for itchy eyes; generally well tolerated, may cause mild eye irritation.
Omeprazole
Widely used acid suppressor for reflux and ulcers; long‑term use needs monitoring for B12, magnesium, bone density.
Omalizumab (Xolair)
Reduces allergic responses in severe cases; risk of injection‑site reactions and rare anaphylaxis.
Ocrelizumab (Ocrevus)
B‑cell depleting therapy for MS; infusion reactions and infection risk require monitoring.
Ondansetron
Common, effective antiemetic; caution with QT prolongation and serotonergic drug interactions.
Oseltamivir (Tamiflu)
Oral antiviral for flu; most effective if started within 48 hours; nausea is a common side effect.
Ofloxacin
Broad‑spectrum antibiotic; risk of tendonitis, neuropathy and QT prolongation; reserve based on guidelines.
Oxcarbazepine
Anticonvulsant related to carbamazepine; can cause hyponatremia and dizziness.
Oxazepam
Short‑to‑intermediate benzodiazepine useful in liver impairment; risks include sedation and dependence.
Oxacillin
Used for penicillin‑resistant staphylococcal infections (not MRSA); watch for allergic reactions.
Oxaliplatin
Key drug for colon cancer; notable for cumulative peripheral neuropathy and cold sensitivity.
Oxandrolone
Anabolic agent used for weight gain and wasting; potential androgenic effects and liver toxicity.
Oxaprozin
Long‑acting NSAID for chronic pain; watch for GI bleeding, renal and cardiovascular risks.
Oxymetazoline
Fast‑acting topical decongestant; limit use to ≤3 days to avoid rebound congestion.
Oxymorphone
Potent opioid analgesic; high risk of respiratory depression, dependence and misuse.
Oxycodone
Common prescription opioid for pain; monitor for sedation, respiratory depression and potential abuse.
Oxybutynin
Reduces bladder spasms; anticholinergic side effects include dry mouth, constipation and blurred vision.
Ozenoxacin (Xepi)
Topical antibiotic for impetigo; minimal systemic absorption, local irritation possible.
Oxiconazole
Cream for tinea and candidal skin infections; may cause local irritation.
Ospemifene (Osphena)
Oral SERM used for painful intercourse from vaginal atrophy; risk of thromboembolism and hot flashes.
Opicapone
Used with levodopa to extend its effect; may worsen dyskinesia and cause dopaminergic side effects.
Orlistat
Reduces dietary fat absorption; causes oily stools and can reduce absorption of fat‑soluble vitamins.
Orphenadrine
Provides symptomatic relief of muscle spasm; causes drowsiness and anticholinergic effects.
Olsalazine
A prodrug of mesalazine acting in colon; can cause diarrhea and abdominal pain in some users.
Omadacycline (Nuzyra)
Newer tetracycline effective for certain resistant infections; avoid in pregnancy and young children.
OnabotulinumtoxinA (Botox)
Botulinum toxin injection for muscle overactivity and cosmetic uses; risk of toxin spread and swallowing issues.
Ocriplasmin (Jetrea)
Single‑use intravitreal treatment for VMA; may transiently affect vision and cause ocular adverse events.
Oxytocin
Common obstetric drug to stimulate uterine contractions; monitor uterine activity and fetal status closely.
Oxytetracycline
Broad‑spectrum tetracycline; causes teeth discoloration in children and is contraindicated in pregnancy.
Osimertinib (Tagrisso)
Oral targeted therapy for EGFR‑mutant lung cancer; monitor for interstitial lung disease and QT prolongation.
Osilodrostat (Isturisa)
Oral inhibitor reducing cortisol production; risk of adrenal insufficiency and electrolyte abnormalities.
Olaparib (Lynparza)
Targeted oral cancer therapy causing myelosuppression, fatigue, and gastrointestinal effects.
Octreotide
Reduces hormone secretion and portal pressure; can cause GI upset and glucose abnormalities.
Obinutuzumab (Gazyva)
B‑cell directed therapy for certain lymphomas; infusion reactions and infection risk common.
Ofatumumab (Arzerra, Kesimpta)
Used in hematology and neurology; monitor for infections and infusion/injection reactions.
Olodaterol
Once‑daily bronchodilator for COPD; may cause tachycardia and tremor.
Omacetaxine mepesuccinate (Synribo)
Cytotoxic agent for refractory CML; notable for myelosuppression and infection risk.
Ozanimod (Zeposia)
Oral immunomodulator; may cause bradycardia on initiation and increase infection risk.
Obeticholic acid (Ocaliva)
Second‑line therapy for PBC; often causes pruritus and may raise LDL cholesterol.