Isoniazid may make Carbidopa + Levodopa work less well. If you take both, your Parkinson's symptoms, such as stiffness, shaking or slow movement, may not be controlled as well as before. Tell your doctor if you notice your symptoms getting worse after starting isoniazid. Do not stop or change either medicine on your own.
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.