A compost conundrum

This week, moved by some impulse to simplify, I decided to clean out the medicine cabinet. I ended up pulling out about half a dozen packages of medicines and supplements that were past their expiration dates. This wouldn't stop me from continuing to use them, as health experts say that most drugs remain safe and effective long past their expiration dates, but the reason these products expired in the first place is that we no longer use them. Along with various generic medicines, the items included

• A bottle of milk of magnesia (purchased, strange as it may sound, because I read that it could be used as a deodorant. It worked reasonably well, but I discovered that for me at least, its laxative properties are still apparent when it's only applied topically. Don't ask me how it's possible; all I know is that it's a side effect I wasn't willing to live with.)
• A bottle of iron supplements in tablet form, which I had to stop taking because they had the opposite effect from the milk of magnesia (though one helpful friend suggested I should just use both and let them cancel each other out).
• A bottle of biotin supplements in capsule form.

The question now: how to dispose of all this stuff? It's not as simple a question as it sounds. Some people simply flush them down the toilet, but then they just end up in the water supply—and municipal water treatment may or may not be able to remove them. Many sites tell you to return prescription drugs to the pharmacy where they were purchased, but the one time I tried that, the pharmacist told me it was against the law in New Jersey for them to take back any drug once it had been dispensed. Back when Brian was working in a lab, we simply slipped the offending medicines into the biohazard bin for safe disposal, but that's no longer an option. And while I might have considered offering unwanted, still-usable medications on Freecycle to those who could use them, I seriously doubt anyone is going to take bottles that are not only opened but outdated.

I consulted the website of the Food and Drug Administration, which says the recommended ways to dispose of medicines are, in order:

1. Follow the instructions on the label (there aren't any on these packages, so no help there)
2. See if your community has a "drug take-back program" (New Jersey has them for prescription drugs only, so no help there)
3. If all else fails, dispose of them in the trash, after first removing them from their original containers, "mixing them with an undesirable substance, such as used coffee grounds or kitty litter," and then sealing them in a new leak-proof container. The purpose of this is to prevent anyone from swiping them out of your trash and using them inappropriately.

All this struck me as a bit wasteful, and I got to wondering: could any of these items safely go in the compost bin? Not the actual drugs, obviously—who knows what those would do to our garden plants—but the supplements? After all, vitamins and minerals are things you want in your food, and in the soil where it's grown. So intuitively, it seems like adding these things the soil should be good for it. But I also know that garden soil's a very complicated system, so how could I be sure?

Finding a reliable answer to this question proved tricky. I found an article on eHow that says supplements can be ground up and added to compost, but that's hardly a reliable source. Likewise, some folks on the GardenWeb forum thought this was fine, but while they're mostly experienced gardeners, they're not exactly soil scientists. So then I tried looking up the individual supplements, but the results weren't much better. Searching on "can you compost iron supplements" turned up several sources suggesting that this is a reasonable idea, but again, no reliable ones. And "can you compost biotin" and "can you compost milk of magnesia" got no useful hits at all.

So thus far, these three bottles continue to sit out on the bathroom counter while I waffle about what to do with them. I fear that at some point, I may end up just shoving them back into the medicine chest to get them out of the way—which would kind of defeat the purpose of cleaning out the cabinet in the first place.