I will assume that by "MST" you mean morphine sulfate. If that is correct then yes, Fentanyl is approximately 80-100 times stronger than morphine sulfate. 100 mcg/fentanyl equals 10 mg morphine.
Fentanyl and Morphine are both in a class of drugs called opiate narcotic analgesics. Both have different uses but both are very strong narcotics. Fentanyl is commonly prescribed for the most severe pain like acute cancer pain, especially bone cancers. Fentanyl is only prescribed to patients who are already opoid dependant and have shown no response to morphine sulfate.
Potential side effects include respiratory depression, severe hypotension, and circulatory collapse.