Which of the following is true about pharmaceutical grade fentanyl and illegally made fentanyl?
a. Pharmaceutical grade fentanyl is always safe for medical use.
b. Illegally made fentanyl is identical to pharmaceutical grade fentanyl.
c. Both types have the same potency and effects.
d. Illegally made fentanyl may be produced in unregulated conditions, leading to variations in potency and safety.