Robaxacet Muscle Relaxant & Analgesic 18 Caplets Acetaminophen/Methocarbamol Caplets Pain Reliever and Muscle Relaxant For effective relief of back pain associated with muscle spasm, tense neck muscles, strains and sprains. Robaxacet contains an analgesic (acetaminophen) to relieve pain and a muscle relaxant (methocarbamol) to relax tense muscles.