Efficacy/advantages

• efficacy - with a failure rate of 1 in 1000, injectable hormonal contraception is more effective than use of the combined pill and female sterilisation (1 in 200 failure) (1)
  • when administered at the recommended dosing interval the failure rate of progestogen-only injectable contraception is approximately 0.2% in the first year of use. With typical use the failure rate is approximately 6% (2)
    
• ease and convenience of use
• use can be kept secret
• reduced menstrual loss
• independent of GIT function
• independent of small intestine
• not affected by antibiotics
• avoids pass through the liver
• fewer metabolic effects
• can be used when oestrogens contraindicated
• stimulates erythropoiesis - reduces crises in homozygous sickle cell disease
• probable reduction in menstrual disorders and gynaecological disease as for combined oral contraceptive - exception of irregular bleeding - but amenorrhoea generally supervenes with regular use
• reduced incidence of pelvic inflammatory disease

Reference:

• 1) Prescriber (2001), 12 (5), 83-95.
• 2) FSRH (December 2014). Progestogen-only injection contraception.