I don't see any reason why the debit under these circumstances would not go through; the HSA administrator wouldn't have any way to know the individual for whom the prescription was purchased. However, you can only treat as qualified medical expenses amounts paid for you, your spouse, dependents claimed on your tax return or dependents you could have claimed on your tax return were it not for the fact that a) the person filed a joint return, b) The person had gross income of $4,050 or more, or c) you, or your spouse if filing jointly, could be claimed as a dependent on someone else's tax return.
You can only claim as used for qualified medical expenses those amounts paid during the year for the individuals listed above. To avoid paying ordinary income tax and, if you are under age 65, a 20% early-distribution penalty on the distribution use for someone else's prescription, you would have to have other, qualified medical expenses that you paid during the year (incurred after your HSA account was established) and for which you were not reimbursed that you can apply against the distribution.
