Hello, I Am A 64 Year Old Female And Was

Hello, I am a 64 year old female and was recently put on lisinopril for high blood pressure. I was taking a 10 mg dose daily of the generic for zestril. a small pink oblong-shaped pill. It seemed to be working, at least for about 14 hours of the day. However, being a veteran, the VA sent me a refill of 20mg small, reddish round pill with one side inscripted "420" and the other side inscripted "IG". This pill is not scored, so I cut them in half to get the 10mg dose. However, I have seen no benefit to my blood pressure reading with this latest pill. It seems the providers are different. Why would one work and the other not? Thank you for your time.