Possibly, you should have a prescription or statement from your doctor to be able to deduct. Don't forget the cost of set up, plumbing and ect. You will need to itemize deductions in order to get a benefit.
Any legitimate medical expense, if proven, can be deductible. Be prepared for the IRS to audit you and demand very definitive proof for a hot tub, though.
In the case of people who require a hottub for medical reasons this may be true. I'm sure that it would hold true for hospitals and/or convalescing homes where the elderly suffer from arthritis.
