Acetaminophen has a therapeutic index of close to 8, much better than chloroquine.

Two points on the topic of OTC drugs in the US:

1. Unfortunately you can buy Lithium as a supplement in the US. I have seen bottles of it for sale on Amazon.

2. Having seen enough accidental (not to mention intentional) overdoses from Acetaminophen, I wouldn't be so fast to act like the therapeutic index is wide enough to be treated as "safe". Anything with a narrow therapeutic window needs to be weighed carefully before use. I hope your take away from my comment wasn't that I think chloroquine is "safe": merely that there are a lot of drugs with narrow windows, and there are trade-offs associated with their use. I included that paper because it discusses this very explicitly.

You are correct that there is a "gray market" for some compounds. The FDA won't come after you for selling lithium carbonate as long as you're not touting it as a medicine. I assume that if it became widespread enough and people got injured, those products would be pulled off the market pretty quickly.

My comments of the TI for acetaminophen was more that it was larger than that for chloroquine. No drug is "safe", but some are safer than others.

TCAs barely used any longer.

Acetaminophen doesn’t belong in this conversation with the other drugs.

I don't see why not? It's a good example where the max therapeutic dose (4000mg/day) is within 2X of the toxic dose range (7500mg-10000mg/day). And even the max therapeutic dose can be toxic to the liver.

And it's exceptionally easy to accidentally overdose if you don't read product labels, since you could be taking multiple products that contain it.

It doesn’t belong in convo with other drugs because it requires far less monitoring. It’s also not taken chronically like the other drugs. Or shouldn’t be, at least.

Acetaminophen overdose is the leading cause for calls to Poison Control Centers (>100,000/year) and accounts for more than 56,000 emergency room visits, 2,600 hospitalizations, and an estimated 458 deaths due to acute liver failure each year.Data from the U.S. Acute Liver Failure Study Group registry of more than 700 patients with acute liver failure across the United States implicates acetaminophen poisoning in nearly 50% of all acute liver failure in this country. Available in many single or combination products, acetaminophen produces more than 1 billion US dollars in annual sales for Tylenol products alone. It is heavily marketed for its safety compared to nonsteroidal analgesics. By enabling self-diagnosis and treatment of minor aches and pains, its benefits are said by the Food and Drug Administration to outweigh its risks. It still must be asked: Is this amount of injury and death really acceptable for an over-the-counter pain reliever?

https://www.ncbi.nlm.nih.gov/pubmed/15239078

If you think acetaminophen is qualitatively the same as warfarin or lithium, you need to go to med school.

That said, any physician who sees a patient taking 4g of acetaminophen a day chronically is going to tell them to reduce their dosage, switch to another drug, or stop.

It’s not safe in the long run.