Doxycyline

I have a cavalier king charles she is just 1 year old and they have performed a tick serology and says she has lymes.
The doctor perscribed Doxycyline .5ml orally twice a day.  Is this going to have any side affects and what should I expect she is only 17 lbs. and seems healthy running and playing can this cure the problem

[Aleda M Cheng, D.V.M., C.V.A]

Doxycycline is a great drug.  The usual side effects are gastrointestinal (vomiting and diarrhea).  Since your dog is only a year old,  her chance of having had a prior undetected bout of Lyme disease is pretty low.  Therefore, the doxycycline hopefully should be curative.