No, it wont cause him harm, but watch out for aversion to his water. He may become dehydrated if he notices something "off" about his water as he may stop drinking completely or not as much. I feel for your room mates. Male mice can be quite... potent... If the vanilla doesnt work, and the only other option for you ends up being dropping him off at a shelter that will likely euth him before he can get adopted, ask your vet to neuter him. I had 5 mice I had neutered. 2 did not make it becuse they had silent pneumonia in both lungs. You mouse must be very healthy because its a big risk for such a small creature, but let me tell you it GREATLY helps with the smell! I did not even do it to reduce smell, I did it because I felt bad that they had to be kept alone (as male mice do 99.9% of the time) and wanted to get them some girl friends. The reduced smell was an unexpected extra benefit.
