Inhalation: You can totally just sniff it from the bottle, but this is a very thick oil. DO NOT USE IN A DIFFUSER.
One potential safety issue is that it contains a small percentage (0.5-1.5%) of caffeine. The amount of caffeine that would get into the body from using 1 drop of coffee oil with 1% caffeine (0.04 mg caffeine) is 2500 times less than from an average cup of coffee (100 mg caffeine) so even those who are hypersensitive to caffeine are not likely to have a problem. As far as caffeine is concerned, it is certainly safe in pregnancy.