To contraindicate is to advise against. You'll almost always find this word in a medical context. A medicine that makes you sleepy would contraindicate driving, but that same medicine would be fine to take while you’re lying on the couch.
Contraindicate has Latin roots in contra for “against” and indicate for “to point out.” To contraindicate means to “point away” because the combination of the activity with the drugs or treatment could be dangerous to the patient. For example, the diagnosis of a virus in a young child contraindicates the use of aspirin because it's been shown to increase the risk of a potentially fatal syndrome. Contraindicate is often used in the passive voice, “For young children, aspirin is contraindicated.”