United States
Usually: Most health plans don't pay for planned treatment abroad.
HSA or FSA funds
Money in a health savings or flexible spending account can usually pay for medical care received abroad, if the treatment is legal in the US. Some travel costs can qualify too.
IRS Publication 502 ↗Employer medical-travel benefits
Some self-funded employer plans pay for treatment abroad, and sometimes travel, because it saves them money. Ask your HR or benefits team.
Tax deduction
Large medical bills, including care abroad, may be deductible if you itemise. Ask a tax adviser.