If you are currently being treated with any of the following medications, you should not use eucalyptus without first talking to your healthcare provider.

5-Fluorouracil
In an animal study, topical eucalyptus oil enhanced the absorption of topical 5-fluorouracil, a medication used to treat cancer.

Others
Eucalyptus may increase the clearance of pentobarbital, a barbiturate used for seizures, and amphetamine, a stimulant used for narcolepsy and, sometimes, attention deficit/hyperactivity disorder. This means that these medications may be eliminated from the body more quickly than they are supposed to be.