is it taxable if PhD student accepts teaching assistantship with full waiver & stipend

His health insurance probably has nothing to do with the med school. Most colleges offer a health plan for students (through a health insurance company). Students who can’t prove health insurance coverage that meets certain rules (set by the college) are required to purchase the plan through the college. Costs vary, usually $1500-2000 per year, although I noticed one that was a whopping $4000 per year recently.