Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
FLEXERIL vs ALTAVERA
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Cyclobenzaprine is a centrally acting muscle relaxant that acts primarily at the brainstem, reducing tonic somatic motor activity via inhibition of descending serotonergic pathways. It is structurally related to tricyclic antidepressants and exhibits anticholinergic, sedative, and analgesic effects.
Combination of ethinyl estradiol and desogestrel: ethinyl estradiol suppresses gonadotropin release, inhibiting ovulation; desogestrel (progestin) causes cervical mucus thickening and endometrial atrophy, preventing implantation.
Adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions (FDA-approved),Off-label: Fibromyalgia, chronic muscle spasm, tension headaches, and as a sleep aid
Prevention of pregnancy,Treatment of moderate acne vulgaris (in females ≥15 years with no contraindications)
10 mg to 15 mg orally three times a day; maximum daily dose: 30 mg.
1 tablet (ethinyl estradiol 0.03 mg / levonorgestrel 0.15 mg) orally once daily for 21 days, followed by 7 placebo days.
Terminal elimination half-life is 18 hours (range 8–37 hours) with clinical context: requires dose adjustment in hepatic impairment; steady-state reached in ~3–5 days.
Levonorgestrel: terminal elimination half-life 25±10 hours; ethinyl estradiol: 13±7 hours. Clinical context: steady-state concentrations achieved within 5-7 days; contraceptive efficacy requires consistent daily dosing.
Primarily hepatic via CYP3A4, CYP1A2, and CYP2D6; undergoes N-demethylation and glucuronidation. Active metabolite: norcyclobenzaprine.
Ethinyl estradiol: primarily metabolized by CYP3A4; undergoes sulfation and glucuronidation. Desogestrel: rapidly converted to active metabolite etonogestrel via CYP2C9 and CYP2C19; further metabolism by CYP3A4.
Primarily hepatic; approximately 50% excreted in urine as metabolites, less than 1% unchanged; 40% excreted in feces via bile.
Renal excretion of metabolites and unchanged drug: ~30% (levonorgestrel) and ~20% (ethinyl estradiol) in urine; biliary/fecal elimination: ~40-50% as conjugates and metabolites.
~93% bound to plasma proteins, primarily albumin.
Levonorgestrel: 98-99% bound to sex hormone-binding globulin (SHBG) and albumin; ethinyl estradiol: 98% bound to albumin.
~14 L/kg (range 10–20 L/kg), indicating extensive tissue distribution.
Levonorgestrel: Vd ~1.8 L/kg (suggesting extensive tissue distribution). Ethinyl estradiol: Vd ~2.4 L/kg.
Oral: ~33% due to extensive first-pass metabolism.
Oral bioavailability: levonorgestrel ~100% (nearly complete); ethinyl estradiol ~45-50% (first-pass hepatic metabolism).
No specific dosage adjustment guidelines; use with caution in renal impairment due to potential for increased side effects.
No dose adjustment required for mild to moderate renal impairment. Contraindicated in severe renal disease or acute renal failure due to potential fluid retention.
Contraindicated in hepatic impairment; Child-Pugh class A, B, C: no safe dosage established.
Contraindicated in severe hepatic dysfunction (Child-Pugh class B or C). Use caution in mild to moderate impairment (Child-Pugh A); monitor liver enzymes.
Not recommended for use in children under 15 years old; safety and efficacy not established.
Not indicated for use before menarche. For postmenarchal adolescents, same dosing as adults (1 tablet daily, 21/7 regimen) after evaluation of risks.
Use lower starting dose (e.g., 5 mg) and titrate slowly; increased risk of sedation and anticholinergic effects. May not be well tolerated; consider alternative therapy.
Not indicated for postmenopausal women. No specific geriatric dosing; consider increased risk of thromboembolism, cardiovascular disease, and metabolic effects in older women of reproductive age.
None
Cigarette smoking increases risk of serious cardiovascular events from combined oral contraceptives. Risk increases with age (especially >35 years) and with number of cigarettes smoked. Women who use combined hormonal contraceptives should be strongly advised not to smoke.
Should not be used for longer than 2-3 weeks (acute use only),May impair mental or physical abilities required for driving or operating machinery,Central nervous system depression additive with alcohol and other CNS depressants,Anticholinergic effects: caution in patients with angle-closure glaucoma, urinary retention, or prostatic hypertrophy,Cardiovascular effects: risk of arrhythmias, especially in patients with preexisting cardiac disease (tachycardia, QT prolongation),Serotonin syndrome risk when used with MAOIs, SSRIs, SNRIs, or other serotonergic drugs,Hepatic impairment: lower doses recommended
Thrombotic disorders: risk of venous thromboembolism (VTE), stroke, myocardial infarction; discontinue if thrombotic event occurs.,Hepatic disease: discontinue if jaundice or liver function abnormalities develop.,Hypertension: monitor blood pressure; discontinue if uncontrolled.,Carbohydrate metabolism: may affect glucose tolerance; monitor diabetic patients.,Depression: discontinue if significant depression occurs.,Gallbladder disease: increased risk of cholelithiasis.
Concurrent use of MAOIs or within 14 days of MAOI therapy,Acute recovery phase of myocardial infarction,Arrhythmias, heart block, or congestive heart failure,Hyperthyroidism
Thrombophlebitis or thromboembolic disorders (current or history),Cerebrovascular or coronary artery disease (current or history),Known or suspected breast carcinoma,Estrogen-dependent neoplasia (known or suspected),Undiagnosed abnormal genital bleeding,Cholestatic jaundice of pregnancy or jaundice with prior pill use,Hepatic adenoma or carcinoma (known or suspected),Pregnancy (known or suspected),Hypersensitivity to any component
Alcohol should be avoided due to additive CNS depression. No specific food interactions; take with or without food. Grapefruit juice does not significantly interact, but caution with high-fat meals may alter absorption slightly.
No significant food interactions. Alcohol does not affect efficacy but may increase risk of adverse effects such as nausea. Grapefruit juice has no known interaction. Avoid excessive alcohol consumption due to potential hepatotoxicity.
Pregnancy Category B. Animal studies have not demonstrated fetal risk, but no adequate human studies in pregnant women. Use only if clearly needed. First trimester: no known risk. Second trimester: no known risk. Third trimester: potential for neonatal adverse effects such as respiratory depression and withdrawal if used near term.
ALTAVERA contains ethinyl estradiol and levonorgestrel. First trimester: Inadvertent exposure during organogenesis is associated with a very low absolute risk of cardiovascular defects (relative risk 1.2-1.4) and no consistent increase in other major malformations. Second and third trimesters: No known teratogenic effects, but theoretical risks from estrogenic effects (e.g., feminization of male fetus). Postnatal: No increased risk of long-term developmental effects from pregnancy exposure.
Excreted in breast milk in small amounts (M/P ratio not established). Clinical relevance uncertain; however, due to potential for adverse effects in nursing infants, caution is advised. Alternative therapies preferred, especially when nursing a premature or low-birth-weight infant.
Combined oral contraceptives may reduce milk production and quality, especially in early lactation. Ethinyl estradiol transfers into breast milk at low levels (M/P ratio approximately 0.1-0.2), excluding clinical effects in term infants. Levonorgestrel transfer is minimal (M/P ratio ~0.2-0.4). Use is generally avoided in breastfeeding women, especially during the first 6 weeks postpartum. Progestin-only methods are preferred.
No specific dosing adjustments recommended for pregnancy. Use lowest effective dose and shortest duration due to potential neonatal effects. Pharmacokinetics may be altered in pregnancy; however, no dose adjustment guidelines exist.
Contraindicated in pregnancy. No dose adjustment recommended because use is discontinued upon confirmed or suspected pregnancy. Pharmacokinetic changes in pregnancy (e.g., increased hepatic clearance, altered binding proteins) are not relevant for this indication.
Flexeril (cyclobenzaprine) is structurally related to tricyclic antidepressants (TCAs) and shares similar anticholinergic and sedative properties. It should not be used longer than 2-3 weeks due to lack of evidence for efficacy beyond that duration. Avoid in patients with hyperthyroidism, heart block, or recent MI. Concomitant use with MAOIs can cause hypertensive crisis. Onset of muscle relaxation is delayed; therapeutic effect may not be apparent until after 2-4 days. Sedation is the most common side effect and can be used to aid sleep.
ALTAVERA is a combined oral contraceptive (COC) containing ethinylestradiol and levonorgestrel. It inhibits ovulation via suppression of gonadotropins. Counsel patients to take at the same time daily to maintain efficacy. Missed pill management: if missed within 12 hours, take immediately; if >12 hours, take last missed pill and use backup contraception for 7 days. Be aware of increased VTE risk, especially in smokers over 35. May reduce effectiveness of lamotrigine; monitor seizure control. Initiate on the first day of menses or first Sunday after onset.
Do not take for longer than 3 weeks unless directed by your doctor.,This medication may cause drowsiness or dizziness; avoid driving or operating heavy machinery until you know how it affects you.,Avoid alcohol and other CNS depressants (e.g., benzodiazepines, opioids) as they may increase sedation.,Do not stop suddenly if taken regularly; taper dose to avoid withdrawal symptoms like headache or nausea.,Inform your doctor if you have glaucoma, urinary retention, or are taking MAO inhibitors (e.g., phenelzine, tranylcypromine).,Take exactly as prescribed; do not increase dose or frequency.,May cause dry mouth; use sugar-free gum or candy for relief.
Take one tablet daily at the same time each day, with or without food.,If you miss a pill by less than 12 hours, take it as soon as you remember. If more than 12 hours, take the missed pill and use a backup method (e.g., condoms) for the next 7 days.,Smoking increases your risk of serious cardiovascular side effects, especially if you are over 35 years old. Do not smoke while taking this medication.,Seek immediate medical attention if you experience sudden severe headache, chest pain, leg pain/swelling, or vision changes (symptoms of blood clots).,This medication does not protect against HIV or other sexually transmitted infections.,If you are taking lamotrigine or other anticonvulsants, tell your doctor; your seizure medication may be less effective.,Store at room temperature away from moisture and heat.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about FLEXERIL vs ALTAVERA, answered by our medical review team.
FLEXERIL is a Muscle Relaxant that works by Cyclobenzaprine is a centrally acting muscle relaxant that acts primarily at the brainstem, reducing tonic somatic motor activity via inhibition of descending serotonergic pathways. It is structurally related to tricyclic antidepressants and exhibits anticholinergic, sedative, and analgesic effects.. ALTAVERA is a Combined Oral Contraceptive that works by Combination of ethinyl estradiol and desogestrel: ethinyl estradiol suppresses gonadotropin release, inhibiting ovulation; desogestrel (progestin) causes cervical mucus thickening and endometrial atrophy, preventing implantation.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between FLEXERIL and ALTAVERA depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of FLEXERIL is: 10 mg to 15 mg orally three times a day; maximum daily dose: 30 mg.. The standard adult dose of ALTAVERA is: 1 tablet (ethinyl estradiol 0.03 mg / levonorgestrel 0.15 mg) orally once daily for 21 days, followed by 7 placebo days.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between FLEXERIL and ALTAVERA in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. FLEXERIL is classified as Category C. Pregnancy Category B. Animal studies have not demonstrated fetal risk, but no adequate human studies in pregnant women. Use only if clearly needed. First trimester: no known risk. . ALTAVERA is classified as Category C. ALTAVERA contains ethinyl estradiol and levonorgestrel. First trimester: Inadvertent exposure during organogenesis is associated with a very low absolute risk of cardiovascular def. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.