How to choose the right contraception

What it is

The contraceptive injection is a slow-release store (depot) of a synthetic progestogen hormone (medroxyprogesterone acetate). The first injection (into your buttock or arm) is initially given during the first five days of your period (to rule out pregnancy) or within the first five weeks after childbirth. If you're breastfeeding, however, the first injection is delayed until six weeks after delivery. After your first dose, the injection is repeated every 12 weeks, as required.

How it works

The depot progestogen injection works by:

• stopping ovulation in most cycles
  
• thickening cervical mucus so that sperm cannot swim through as easily
  
• thinning the endometrial lining of the womb, so that if an egg is fertilised, it can't implant or develop
  
• decreasing motility of sperm and eggs within the Fallopian tubes.

Pros

• Relieves painful periods.
  
• No serious side-effects.
  
• Can be used during breastfeeding.
  
• Doesn't have to be remembered every day.
  

Cons

• Periods may be frequent, irregular, or absent.
  
• Some women get very heavy, erratic bleeding during the first 3 months of using this method. This doesn't usually continue after the second injection
  
• The injection can't be removed, so any unwanted effects may last for 12 weeks
• There can be a delay in return of fertility after stopping the injection.
  
• Some women gain weight.
• It reduces bone mineral density in many women who use it. This effect is greatest during the first 2-3 years of use. It isn't yet known whether this reduction in bone mineral density increases the risk of osteoporosis and fractures in later life. This effect may be more important in adolescents, as this is time when bone mineral density should be increasing to achieve peak bone mass. The bones start to recover when the injection is stopped, but it isn't yet known whether the bones ever regain full strength