It's usually safe to take eucalyptus oil internally by mouth for up to 12 weeks as long as you do not overdose on the eucalyptus oil internally.
However the eucalyptus oil must be diluted with water first before taking the eucalyptus oil internally.
Failure to dilute the eucalyptus oil before taking it internally can be fatal.
As long as you dilute the eucalyptus oil before taking it internally then you should be safe although it's really not worth the risk.
Because if you're not careful you could potentially overdose on the eucalyptus oil which can and will be fatal.