UK Clinical Pharmacy Association

Norethisterone (at therapeutic doses i.e. > 5mg)

Issues for surgery

For treatment of endometriosis, menorrhagia or dysfunctional uterine bleeding – potential increase in symptoms if stopped.

Risk of venous thromboembolism (VTE) if therapeutic doses continued (see Further information).

Advice in the perioperative period

Elective surgery 

Consider stopping 4 weeks before surgery where prolonged immobilisation is likely (e.g. abdominal surgery or orthopaedic lower limb surgery).


If continuing, ensure adequate thromboprophylaxis as risk of VTE comparable to combined oral contraceptive pill.

Emergency surgery 

Ensure adequate thromboprophylaxis as risk of VTE comparable to combined oral contraceptive pill.

Consider stopping on admission if prolonged immobilisation is likely. 


Post-operative advice

If discontinued pre-operatively, restart once mobile.

Interactions with common anaesthetic agents


Administration of a single bolus dose of sugammadex is predicted to cause a 34% decrease in progestogen exposure. Bear this in mind if there is sugammadex is used perioperatively and there is a failure in norethisterone treatment.

Interactions with other common medicines used in the perioperative period


Further information

Risk of VTE

Therapeutic doses of norethisterone and norethisterone acetate (used for endometriosis, menorrhagia, dysfunctional uterine bleeding or postponement of menstruation) are thought to be associated with an increased risk of VTE. Partial metabolism of norethisterone to ethinylestradiol has been noted at doses exceeding 5mg. A daily norethisterone dose of 10-20mg is likely to equate to a 20-30microgram dose of ethinylestradiol, and therefore carry the same VTE risk as the combined contraceptive pill.

The conversion of norethisterone to ethinylestradiol has been attributed to a structural peculiarity of the norethisterone molecule and thus there are no implications for other progestogens regardless of dose.


Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. [Accessed on 10th May 2019

Faculty of Sexual and Reproductive Healthcare. Clinical Guidance Progesterone-only pills. Clinical Effectiveness Unit. March 2015 (updated April 2019). [Accessed on 11th May 2019]

Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. [Accessed on 11th May 2019]

Mansour, D. Safer prescribing of therapeutic norethisterone for women at risk of venous thromboembolism. J Fam Plann Reprod Health Care. 2012; 38:148-149

Summary of Product Characteristics – Primolut® (norethisterone). Bayer plc. Accessed via 11/05/2019 [date of revision of the text December 2018]

Summary of Product Characteristics - Bridion® (sugammadex). Merck Sharp & Dohme Limited. Accessed via 10/05/2019 [date of revision of the text March 2019]