Yes, ti is safe to give to cats. The dosing is as follows:
Dried extract: 20mg/kg, divided daily. For a 10 lb cat this is 100 mg.
Juice: 1mL/kg per day, divided daily (may be diluted and added to food); use low-sugar products and aim for highest juice concentrate possible. For a 10 lb cat this is 5 mls or one teaspoon.