Release of copper from copper-bearing intrauterine contraceptive devices.

We measured the rate of release from copper-bearing intrauterine contraceptive devices (IUDs) with varying copper surface areas. Over 135 days of observation the release rate decreased exponentially. This decrease in the release rate was associated with the deposition of a protein layer on the surface of the metal. The bioavailability of copper on IUDs was not related to the volume of copper remaining on the device. Consequently any increase in the copper surface area of an IUD is unlikely to affect the duration of its copper-dependent contraceptive action.