Medroxyprogesterone and Ritonavir: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ritonavir
Medroxyprogesterone
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced estrogen/progestin exposure and reduced efficacy of contraceptive
Interaction Deep Dive
COCs have shown significant decrease in plasma concentrations of estrogen and/or progestin during coadministration with ritonavir1. Concomitant use of ritonavir and combination hormonal contraceptives may decrease efficacy of the contraceptive. The AUC of a single 50 mcg dose of ethinyl estradiol declined by 40% on average when given concomitantly with ritonavir 500 mg twice daily. Cmax of ethinyl estradiol also decreased by 32% 2. In a study, the AUC of ethinyl estradiol decreased from 1670 pg/mL/hr to 993 pg/mL/hr when coadministered with ritonavir 3. If concomitant use is necessary, alternate methods of contraception should be considered 2.
Why it happens (mechanism)
Unknown
Literature reports
3 reports — tap to read
a) Twenty-three female study participants received a single oral dose of an oral contraceptive containing ethinyl estradiol 50 mcg and ethynodiol diacetate 1 mg on study days 1 and 29. From days 15 through 30, ritonavir was administered twice daily. Cmax of ethinyl estradiol was 104 picograms (pg)/mL when administered alone, and decreased to 70.7 pg/mL in the presence of ritonavir. Likewise, the AUC of ethinyl estradiol decreased from 1670 pg/mL/hr to 993 pg/mL/hr when coadministered with ritonavir. These results are consistent with an increase in ethinyl estradiol clearance from hepatic enzyme induction of glucuronidation and/or cytochrome P450 hydroxylation caused by ritonavir 3.
b) Ritonavir is an inhibitor of CYP3A4, which is involved in the metabolism of both estrogens and levonorgestrel. As such, inhibition of metabolism may result in increase plasma concentrations of estrogen and/or levonorgestrel and risk of related side effects 4.
c) The AUC of a single 50 mcg dose of ethinyl estradiol declined by 40% on average when given concomitantly with ritonavir 500 mg twice daily. Cmax of ethinyl estradiol also decreased by 32% 2.
Common questions
Can I take Medroxyprogesterone and Ritonavir together?
Reduced estrogen/progestin exposure and reduced efficacy of contraceptive Always confirm with your pharmacist or prescriber before making any change.
How serious is the Medroxyprogesterone and Ritonavir interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Medroxyprogesterone or Ritonavir need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (4)
- Product Information: LOESTRIN(R) 24 Fe oral tablets, norethindrone acetate ethinyl estradiol oral tablets, ferrous fumarate oral tablets. Teva Pharmaceuticals USA Inc (per FDA), Parsippany, NJ, 2023. DailyMed
- Product Information: NORVIR(R) oral soft gelatin capsules, ritonavir oral soft gelatin capsules. AbbVie Inc. (per FDA), North Chicago, IL, 2015. DailyMed
- Ouellet D, Hsu A, Qian J, et al: Effect of ritonavir on the pharmacokinetics of ethinyl oestradiol in healthy female volunteers. Br J Clin Pharmacol 1998; 46:111-116. PubMed
- Product Information: ClimaraPro(TM), estradiol/levonorgestrel transdermal system. Berlex, Montville NJ, 2003.
Keep reading about Ritonavir
Keep reading about Medroxyprogesterone
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