Norethisterone is most commonly prescribed for period delay. The following instructions apply:

Establish when your next period is expected. You need to be able to predict the likely start date of your period with reasonable accuracy.
Start taking norethisterone 3 days before your period is expected to begin. This lead time is essential — if you start taking norethisterone on or after the expected date your period may not be successfully delayed.
Take one 5mg tablet three times daily. Space the doses as evenly as possible throughout the day — for example, with breakfast, lunch, and dinner, or at 8-hour intervals.
Continue taking the tablets for as long as you wish to delay your period, up to a maximum of 20 days total. This provides up to approximately 17 days of actual period delay (3 days lead-in + 17 days delay = 20 days total course).
When you are ready for your period to begin, simply stop taking the tablets. Your period should begin within 2–3 days of your last dose.
If your period does not start within 3 days of stopping norethisterone, you should perform a pregnancy test and contact your GP.

What If I Miss a Dose?

If you forget to take a tablet, take it as soon as you remember. If it is almost time for your next scheduled dose, skip the missed dose and continue with your regular schedule. Do not take two tablets at once to make up for a missed dose. If you are late with a dose and notice breakthrough bleeding or spotting beginning, continue taking the tablets as prescribed — this does not necessarily mean the treatment has completely failed.

⚠  Missed Doses and Period Delay

If you regularly miss doses, or take norethisterone fewer than three times daily, you are at increased risk of breakthrough bleeding (spotting) during the intended delay period. Consistent three-times-daily dosing is essential for period delay to be reliable.

Do NOT use if:

• Hypersensitivity or allergy to norethisterone, any other similar hormonal medicines, or any of the excipients (lactose, maize starch, magnesium stearate). Patients with rare hereditary problems of galactose intolerance, total lactase deficiency, or glucose-galactose malabsorption should not take norethisterone due to its lactose content.
• Pregnancy, or suspected pregnancy. Norethisterone is contraindicated during pregnancy. A pregnancy test must be excluded before starting treatment if any doubt exists. Norethisterone is not teratogenic at clinical doses based on available data, but use during pregnancy is not justified for period delay and should be avoided.
• Previous idiopathic or current venous thromboembolism (VTE) — including deep vein thrombosis (DVT) or pulmonary embolism (PE). A personal history of blood clots is an absolute contraindication.
  Active or recent arterial thromboembolic disease — including angina pectoris or myocardial infarction (heart attack).
• Current or past disturbance of liver function, or active liver disease. Norethisterone is metabolised by the liver; impaired hepatic function may lead to accumulation and toxicity.
• History during pregnancy of idiopathic jaundice (cholestasis of pregnancy).
• History of severe pruritus or pemphigoid gestationis (herpes gestationis — a rare autoimmune skin condition of pregnancy).
• Undiagnosed irregular vaginal bleeding. Any unexplained vaginal bleeding must be investigated before prescribing norethisterone, as hormonal treatment could mask the cause of bleeding or worsen an underlying condition.
• Porphyria (any form) — norethisterone is contraindicated in all porphyrias due to the risk of triggering an acute attack.
• Known, suspected, or past history of hormone-sensitive carcinomas — including carcinoma of the breast (except where specifically prescribed by an oncologist at high dose for disseminated breast cancer treatment) or other hormone-dependent cancers. Gynaecologists advise against use in women with a personal history of genital or breast cancer.