For most persons, health insurance premiums have been a deduction available in Schedule A for at least the last 20 years. Whether a particular person can deduct health insurance premiums depends on the person's particular facts. Most persons with minor medical expenses will not be able to deduct the medical expenses as the thresholds to begin to deduct are high.
In more recent years, for certain self-employed taxpayers, health insurance premiums may be deductible outside of Schedule A.
For the specifics on eligibility, you can read the free Publication 17 from the IRS at www.irs.gov . There is an index at the end of the publication. Or, use the computer's search function on the document.
Or, consult with a local tax professional (CPA, Enrolled Agent, or attorney) to help.