But the medicine may become less effective after several years of use.

It is quite effective with a 3 percent failure rate during the first year of use.

I would tend to accept either for a given year of use.

Most people have fewer side effects after 1 year of use.

After 16 years of heavy use, he stopped in 1983.

This means that about 11-16 women per 100 can get pregnant during the first year of use.

In some cases it has been known to cause cancer within only a few years of use.

It was closed in June 1998 after nearly 150 years of use.

There were no other changes to the site during its years of use.

Rates are generally presented for the first year of use.