If you're looking forward to getting Medicare because you think this health insurance for seniors will provide comprehensive coverage, you may end up disappointed. Studies have shown seniors with high-prescription drug needs could incur as much as $350,000 in out-of-pocket spending on healthcare during retirement, even with both Medicare and a supplementary Medigap policy.

You need to be as prepared as you can for high healthcare costs as a senior, and that starts with understanding the kinds of healthcare services that Medicare won't pick up the tab for. Here are seven you should be aware of.

1. Chiropractic care and most alternative treatments

Even though about half of all older adults experience some degree of back pain, Medicare won't cover chiropractic care or acupuncture to help manage or eliminate discomfort.

While Medicare will cover spinal manipulation when necessary to correct a misalignment in the spine (called a subluxation), routine chiropractic care to stay healthy -- which is called maintenance care -- is not paid for. Acupuncture and many other alternative and holistic treatments are also not covered at all.