Is it safe to take 8000 mg of methocarbamol?

Usually not: Assuming this is orally given for muscle spasm (it can be given IV and also be used for tetanus), you can take up to 6 gms/day (split up 4x/day, therefore 1.5 gm/dose) for the first 2-3 days, then decrease to 4-4.5 gms/day in 3-6 divided doses. There are rare cases where you can take 2 gms/dose during the 1st 2-3 days (discuss with md 1st). Confusion and low heart rate & blood pressure=toxicity.