In the UK there are soon to be four different POPs: desogestrel (DSG) 75 μg, drospirenone (DRSP) 4 mg (this is a new) and the ‘traditional’ POPs levonorgestrel (LNG) 30 μg and norethisterone (NET) 350 μg

Contraceptive effectiveness: As with all oral contraception, POPs are user-dependent. If used perfectly, POPs may be more than 99% effective; but with typical use, risk of pregnancy during the first year has been estimated at about 9%. Contraceptive effectiveness can also be affected by drug interactions (eg, concomitant use of enzyme inducing drugs) and by malabsorption. 

How to take POP (and what to do if use has been incorrect). LNG, NET and DSG POPs are taken continuously at 24-hour intervals. The DRSP POP is taken in a regimen of 24 daily active pills followed by four hormone-free placebo pills. All POPs should be taken at the same time each day. LNG and NET POPs are considered missed if taken more than 3 hours late, a DSG POP if it is taken more than 12 hours late, and a DRSP POP if more than 24 hours late. Note that recommendations for DRSP POP differ from those for other POPs. 

Who can and cannot use POP? All POPs can be used by medically eligible individuals between menarche and age 55 years. Contraindications are: ischaemic heart disease, history of stroke, breast cancer (current or past), severe cirrhosis, hepatocellular adenoma or carcinoma. DRSP is an aldosterone antagonist thus there is potential risk of hyperkalaemia in susceptible individuals. 

Drug interactions: Drugs that induce hepatic enzymes increase metabolism of progestogens and could reduce contraceptive effectiveness of POPs. POPs use could reduce effectiveness of ulipristal acetate (UPA) for emergency contraception (EC).  Pharmacodynamic interaction between the DRSP POP and drugs such as angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists could also potentially increase risk of hyperkalaemia. 

Health risks: Very limited evidence suggests no increase in risk of venous thromboembolic events, thrombotic stroke or myocardial infarction (MI) associated with use of POPs and no significant effect on risk of endometrial cancer, ovarian cancer or breast cancer. Compared to use of no contraception, use of all effective methods of contraception, including POPs, reduces risk of ectopic pregnancy. 

Side effects: Unpredictable bleeding/spotting is common with use of all POPs. For problematic bleeding during use of a DSG POP some clinicians offer use of a double dose (150 μg daily) but there is not yet robust published evidence of the effectiveness of this strategy. Evidence is too limited to confirm or exclude any causative association between POP use and headache, acne, libido, weight gain or mood. 

Non-contraceptive benefits: In practice, some clinicians offer DSG POP (or double-dose DSG POP) for management of heavy menstrual bleeding but there is not yet robust published evidence to inform effectiveness for this indication. DSG and DRSP POP could reduce dysmenorrhoea for some users. 

Starting POP: LNG, NET and DSG POPs can be started on days 1-5 of a natural menstrual cycle, by day 5 after abortion or by day 21 after childbirth without requirement for additional contraceptive precautions. At any other time, these can be quick started with advice to use additional contraceptive precautions for 2 days and to take a follow-up pregnancy test if required. In contrast (reflecting manufacturer guidance for the new DRSP POP) this guideline recommends that additional contraceptive precautions are required unless DRSP POP is started on day 1 of a natural menstrual cycle, day 1 after abortion or by day 21 after childbirth. If started at any other time, additional contraceptive precautions are required for 7 days with advice to take a follow-up pregnancy test if appropriate.