I have an interview on Monday

[Nikia]

I called back the person who left a message about the job. She called me back. I understood most of what she said (She was the one with a thick accent.)and was able to answer all of her questions about my experience. She is the head of the department. I will be interviewing with her and two other people.
The company manufactures dietary supplements. The position is for a microbiological technician who is entirely responsible for their lab and all the testing and equipment and supplies.
What should I wear? I do have a navy blue dress suit, but I have felt overdressed in past interviews and was told by a female boss at a previous job that women in manufacturing should wear pants.
I smoke pot. She did not say anything about drug testing. One of the products that they make is a detox, as in pass the drug test, formula. Should I refrain from smoking until the interview process is over and buy their detox formula or should I assume that such a company would not be contradictory in this way?
This is my first interview in a long time. I have had my current job for two and a half years and have been very unhappy there. I have not interviewed since. Any advice?

[Baclava]

1. Just...

Smile...and act confident.

[Sagan]

2. lay off the smoke

At least until you know if they're going to drug test you or not. They won't do it immediately after an interview in any case.

Wear the suit. If they haven't said what to wear, you should always wear the best you have.