One note about using HSAs to pay for medical expenses: you can use funds in an HSA to reimburse yourself for qualified medical expenses that you incurred at any time since you started the HSA. There is no time limit to this. As long as you keep records around in case you get audited, you can keep the money in the HSA earning investment income tax free until you absolutely need the money, which might be decades in the future. Because this is my plan, I didn’t bother with getting an HSA debit card - I don’t plan on withdrawing the money any time soon, because I don’t need the money and am building up money in my taxable investment account even having to pay for all my medical expenses out of pocket. The two reasons why you wouldn’t do this is that you don’t have the money to spare outside the HSA, or you don’t want to have to keep records for decades on just how much you’re allowed to withdraw tax free.
I’ll also mention that once you turn 65, you can treat the HSA just like a traditional IRA; there is no longer the 20% penalty for withdrawing funds and not using them for medical expenses. You pay income tax on whatever you withdraw that’s not for medical expenses, but considering you didn’t pay tax on the amounts you contributed, that’s perfectly fine, and is the same way an IRA works.
If you have a ton of medical expenses, you can also cheese the system in place that discourages excess contributions to HSAs. If you contribute to your HSA more than allowed, for whatever reason that might be, like both spouses’ employers contributing the family amount, you pay 6% per year on the excess contributions until you rectify the issue by not contributing as much in future years. However, the tax is capped at 6% of the balance of your HSA at the end of the year. Thus, you can contribute as much as you want to your HSA, and not even be on a HDHP, and you won’t pay a dime in penalties if you spend it all. Of course, since you won’t be able to deduct any more than you’re “allowed” to contribute, you won’t be able to get excess benefits out of this from personal contributions other than possibly the investment income from the beginning of a year until the end. However, it does mean that in the case where both spouses have employers contributing the family amount, there’s no penalty as long as you spend it all by the end of the year on medical expenses. I had a client that fell into this situation, and I was rather surprised at the outcome. I did inform them that they would either need to get their employers to reduce the amounts they were contributing, or make sure that they emptied the account by the end of the year. That obviously requires a significant amount of medical expenses, so it’s not for everyone.
As to what you can use the HSA funds on, it’s generally the same as anything that is allowable as a deduction for medical expenses. A recent development in this is that personal protection equipment to help prevent the spread of the coronavirus is allowable, whereas normally it would only be allowed if you actually needed it once you were infected. You can find a mostly full list of things in IRS Pub 502. However, since the CARES act, for HSAs (and FSAs, but that’s not the topic), there are now allowed over-the-counter medication and menstrual care products that are not generally allowed as deductible medical expenses based on Pub 502. This was retroactive to the beginning of 2020, so if you had such expenses before the law was passed, or before stores allowed them to be put on debit cards since the law required some time to implement, you can request reimbursement for them now.
Vitamins are acknowledged as a grey area. The phrase that governs this is that it has to be for “the diagnosis, cure, mitigation, treatment, or prevention of a disease and cannot be “merely beneficial” to the general health of an individual.” I would only include vitamins in your HSA allowable expenses if they are recommended to you by a health care professional whose care you are under for a specific problem. For instance, I take Vitamin D at the recommendation of my psychiatrist, so I include whatever I pay for that in my HSA eligible expenses, because my assumption is that the Vitamin D is part of the treatment plan she has for my mental illness. My mother takes a ton of vitamins for reasons of her own design, and so I wouldn’t suggest that she able to pay for those with an HSA, even if she thinks that she’s treating or preventing something specific, though this is definitely a grey area and an argument might be able to be made on a case-by-case basis (she takes at least 6 different supplements). If my internal medicine provider would recommend a multi-vitamin because I didn’t eat enough vegetables or whatever, I don’t think that would count - there’s no direct connection between a specific health issue and the reason that the vitamin is taken.