The substance gave zero benefit to Elizabeth's character, she just slept for a week without any of Sue's experience and only had the negatives of when she was late with the spinal fluid, and that she loses precious time being asleep half of every month. If she couldn't experience the youth then it makes the substance pointless for her character to take it at all. It's an entertaining movie but the concept is poorly executed, great practical effects though, pretty sure they weren't CG.