There are prescription medications that have been used in the past and are still used in very rare circumstances, but they are generally not recommended since there are serious health risks associated with their use.The safest way to wean is to make it a gradual process, eliminating one daily feeding at a time, then waiting a few days for your body to adjust before eliminating the next one.
There are a couple of natural ways to help decrease your milk supply as you slowly eliminate feedings:Mint: Peppermint oil helps to reduce milk supply. Mint tea or breath-mints that contain pure peppermint oil (such as Altoids) can be a pleasant way to help ease your supply a bit.
Sage: Many health food stores carry sage capsules. These can be helpful in reducing milk supply as you wean. You can also try sage tea.
In some cases moms have used over-the-counter decongestants to help lower milk supply, but discuss this practice with your doctor first to make sure it's a safe option for you.