Drug Rehabilitation that works

I’ve been using Meth for two years. I went to rehab in December and I’ve been seeing a pshychiatrist since I got out. She prescribed me Lamictal for my bi-polar and I was taking it as prescribed for a month. I relapsed a week ago though and stopped taking my medication because I didn’t want to combine the two. I know that the medication is still in my system though and then Meth was as well. What are the effects of the combination of Lamictal and Methamphetamine? What kind of harm to my brain am I causing? What can happen?

This is just one of those questions I had that just popped into my head. I am just curious to what happens after you snort the crystal meth (inside the body), not smoke it or inject it.