Do inform your therapist if you are under any medication or are allergic to any thing. Also select a therapist with necessary qualifications to administer the massage.
Some conditions where it must be avoided are as follows:
Thrombosis of Veins (blood clots)
Skin conditions like eczema or other contagious conditions
Recently healed fractures
Recent surgical procedures
Pregnancy (subject to which area to be treated and which month)
Certain abdominal conditions
Go ahead and Relax and Rejuvenate!!