My manager threatened to fire me unless I stopped taking Chantix

[Digit]

I work for a large corporation, and my direct manager said this.

I have high blood pressure already, and had already tried the patch, which did not help. I just continued smoking while using the patch.

I did pretty well on Chantix before, but quit because of the nausea. I was down to about 3 ciggies a day, but I began to get dry heaves when my dose was increased.

This time, I wanted to just keep on the lower dose and figured I could quit by just taking it alittle longer.

I had warned my manager that I was going to be taking Chantix and if I became loopy, it was due to that.
By loopy, I mean forgetful.

Well, I read my work schedule incorrectly and came in a half hour late two days in a row. On the dot. I had never been late or missed a day of work. He did not mention it to me the first day, and I had no idea I had done anything wrong. I did it again the second day, and he said I had to quit the Chantix or be fired. I thought he was joking and I rechecked the schedule and he was correct. I don't know how in the world I read it wrong, but by not pointing my lateness out the first day, I had no clue I was doing something wrong.

Of course Chantix is only by doctor's prescription and my health insurance is through my employer.
Do I go back on it on the Q-T and not say anything or risk going to HR?