Yes, you can use Nalfy as a substitute. Nalfy is a brand name for Nalbuphine hydrochloride, meaning it contains the exact same active medication. However, before making the switch, please consult your pharmacist or doctor to ensure the dosage strength and administration method match your original prescription. Because you are treating chest pain, close monitoring is essential. If your chest pain worsens, radiates to your arm or jaw, or is accompanied by shortness of breath and sweating, please seek emergency medical attention immediately.