Cardarine GW is very mild in the way of side effects. It is not a hormone or a stimulant so there are no issues of cortisol increases or testosterone suppression. It is safe to use by females because it is non-hormonal.
The only side effects your might experience are an increase in sweating during your workout due to the endurance increasing properties the SARM causes.
You can read up more on cardarine here:
http://www.evolutionary.org/cardarine/
I recommend a dosage of 10-20mg/day for 12-16 weeks before taking a 4 week break. After the 4 week break you can do another cardarine cycle.