2 Research recommendations
The scarcity of robust evidence to answer important clinical questions on the use of LARC methods by women in the UK posed great challenges to the developers of the original guideline (October, 2005). In the majority of cases, the guideline recommendations were based on extrapolated evidence that is indirect or of poor methodological quality. In 2005, the Guideline Development Group made the following recommendations for research on the basis of its review of the evidence.
In making these recommendations for research, the guideline developers consider it important and relevant that the research should be specific to the UK population because there are cultural differences in the response to side effects and non‑contraceptive effects of hormonal contraceptives. In addition, freedom to choose any contraceptive method and the provision of a free contraceptive health service in the UK can influence important outcomes such as continuation rates and patterns of method switching.
Few women use contraception perfectly (that is, exactly in accordance with the product instructions) and consistently. Pregnancy rates during typical use reflect effectiveness of a method among women who use the method incorrectly or inconsistently. Few data are available on typical use of any contraceptive method among women in the UK. Much of the data on contraceptive effectiveness used in the guideline come from clinical trials or surveys undertaken in other countries such as the USA. Large prospective cohort studies are needed to compare the contraceptive effectiveness of LARC methods with non‑LARC methods during typical use in the UK. 
Most women will need to use contraception for more than 30 years. Patterns of contraceptive use vary with age, ethnicity, marital status, fertility intention, education and lifestyle. Large prospective cohort studies are needed to identify:
patterns of use (initiation, continuation and switching between methods) of LARC methods compared with non‑LARC methods
factors that influence the patterns of use of LARC. 
In addition to individual circumstances and needs, a woman's choice and acceptance of LARC may be influenced by potential health disbenefits (side effects and risks) as well as non‑contraceptive benefits of LARC (such as alleviation of menorrhagia). Large population studies of appropriate design are needed to determine the effect of these factors on the uptake of LARC methods and the implications for NHS resources. 
The effect of injectable contraceptives on bone mineral density in women who have used DMPA for longer than 2 years is uncertain. Adequately powered surveys or cross‑sectional studies are needed to examine the recovery of bone mineral density after discontinuation of DMPA after long‑term and very long‑term use. Studies are also needed to examine the risk of bone fractures in older women.