Any time a doctor suggests a new prescription, be sure to talk about what other medicines, supplements, herbs, and vitamins are already being taken. Sometimes one kind of medicine changes the way another kind of medicine works in the body. If two kinds of medicine affect each other, the doctor may prescribe something else or change the amount to be taken.

How does Topamax affect other medicines?
Topamax makes birth control pills less effective, so the chances of becoming pregnant are greater. Women who use pills for birth control should talk to the doctor who prescribed them right away if they start taking Topamax. The same is true for some other forms of birth control such as Depo-Provera or implants. Topamax does not affect barrier types of birth control, like condoms, IUDs, and diaphragms.

Topamax also affects the way the body handles phenytoin (Dilantin, Phenytek). Topamax may increase the level of phenytoin, particularly if the level of phenytoin is already at the upper end of the therapeutic range (the level that is usually effective without causing excessive side effects).

How do other medicines affect Topamax?
Because Topamax is broken down (digested) in the liver, it may be affected by other seizure medicines that speed up the ability of the liver to digest drugs.

The seizure medicines that may reduce the level of Topamax in the blood:

• carbamazepine (Tegretol, Tegretol XR, Carbatrol)
• phenytoin (Dilantin, Phenytek)
• phenobarbital
• primidone (Mysoline)

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