Like most GPs, I’ve happily dished out prescriptions for norethisterone when a woman wanted to postpone her period, on a basis of hey, what harm can it do? More than I thought, it turns out; according to an article in April’s JFPRHC, norethisterone is actually metabolised to ethinylestradiol, and taking 5 mg tds is therefore equivalent in terms of thrombosis risk to taking a 30 mcg COC. In most cases, of course, this won’t matter, but it does mean that giving norethisterone doesn’t have any benefits over the COC as far as risks go.
This has the following implications:
- If a woman who wishes to postpone menstruation can safely take a COC, she might as well just do so; it’s simpler to take than norethisterone and doesn’t have the anecdotal side-effect of causing heavier bleeding when the period does start. (The exception, I suppose, would be if she had had previous side-effects with COCs and wished to try something different.)
- If a woman who wishes to postpone menstruation is at increased thrombosis risk, then her best option is probably to try 10 mg methylprogesterone three times daily started ‘before the onset of menstruation’ (it doesn’t say how far before). There is no published evidence to support its use and, anecdotally, it may be less effective than norethisterone, so it’s really just a case of doing something just in case it helps.
The article also had an interesting list of the percentage of women achieving amenorrhoea over a 90-day reference period on various contraceptives:
- Mirena – 23.6% at 3 years
- Jaydess – 11.6% ‘over time’
- Nexplanon – 20% ‘over time’.
- Depo-Provera – 55% at 12 months
- Sayana Press (new form of injectable DMPA) – 56.5% at 12 months
- Standard COC in 21/7 regime – <1%
- Estradiol COC with shorter hormone-free break – 19.4 – 31% ‘over time’. (Interesting. Didn’t know that.)
- Desogestrel POP – 20% at 12 months. (I’d always been told it was 50%, so I guess that must be over a longer time period? Or maybe I’ve just been told wrong!)
- Traditional POPs – 3% at 12 months (again, I’d been told 10% overall, so hopefully few more over time).