Taking Zoloft with codeine at the dose you did will not cause permanent brain damage.
It is generally advised that the total daily dose of codeine should not excedd more than 60 - 100mg. In your case,6 8mg tablets makes only 48mg per day.
Combined wih Zoloft 100mg, this can cause sedation and long term use can cause some amount of depression but no, it will not cause permamnent brains damage.
I hope this helps.
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