How normal would it be for seroquel (quetiapine) to cause slurry speech, difficulty talking?

Possibly : Seroquel (quetiapine) could cause those symptoms but you would usually expect the dose might be too high or had interacted with another medication. It can cause involuntary motor movements which if they involved the mouth could affect speech. If those symptoms are sudden in onset a more serious cause like stroke needs to be considered and needs to be evaluated immediately in an er. If not the call provider.