Dr. Ouyt me on McKenna shot...anyone else on it?

My doctor started me on the McKenna shot yesterday to help prevent preterm labor. My oldest son, who is now 16, was born 8 weeks early. Then when I was pregnant with my youngest, who is now 14, they put me on a pill to prevent preterm labor. The pill worked because he was full term but it had some bad side effects. The pill made me feel like my heart was going to beat out of my chest. My doctor told me that they no longer give that pill because of that. She told me that this shot doesn't have any side effects. I'm just curious if anyone has any experience with this shot. It has been 14 years since the last time I was pregnant so things have changed lol.