Inquiring minds want to know.
How old ?
What conditions did they age into crumbling? Steamy bathroom, etc.
Potency of the API aside, a change in the formulation like that can change the pharmacokinetics of how the drug is absorbed into the body and how long it lasts. Though depending on the exact molecule, that half-life might be long enough to not make much difference. Safer to discard the medication.
average age 4-5 years. normal storage conditions. crumbling due to age.
That long over ‘use by’ date I would pitch them and call for a new script.
Don’t be surprised if that new script is harder to get. A lot has changed about benzo prescribing in the last 5years.
Hey I took one yesterday, I’m fine 
I think the binding agent deteriorates and that’s what causes the crumbling. who cares
I can offer authoritative empirical data about what happens when the stuff is really old! 
I once found an old Valium tablet that could be described as “crumbling and powdery”, from an old prescription that was many decades old and obviously many decades expired. Valium (diazepam) is one of the most common benzodiazepines. I took it one night when I was having trouble sleeping.
The good news is, nothing bad happened. The bad news is, nothing happened at all. It had completely lost its potency.
IANAD or a pharmacist but there is always an outlying chance that a drug could have morphed into something potentially harmful, so in general I think old expired drugs should be thrown out. In this case Valium is so (relatively) innocuous that I didn’t think it was much of a risk. But @BippityBoppityBoo is right – diazepam and its brethren are out of fashion these days and most doctors are reluctant to prescribe them. They were once one of the most commonly prescribed drugs but too many people abused them and got addicted.
wow that was kind of ballsy of you lol. and I thought I was bad ass…
Night nurses invented bad ass.
Given that it was a tablet originally, this crumbling seems irrelevant to the efficacy of the medication. Tablets are designed to crumble or dissolve once in the stomach. And a good share of patients chew tablets before swallowing them, anyway. It used to be common to have medications as powders or liquids that the patient took via a measured spooned amount.
Unless the tablet was coated or encapsulated some way, it seems like the active ingredient shouldn’t be affected by this – it’s all the same once it gets into the stomach.
But the age might have some effect – some medications do become less effective over time.
You know what stays effective? Codeine. I have some codeine cough syrup that is decades old. The only problem is that some of the alcohol it was dissolved in has evaporated, so it’s a little stronger per teaspoon than it used to be.
I take a spoonful or two every several years when I have a really bad cough and can’t sleep. It’s obvious that it’s still good, because it immediately (but very briefly) numbs the throat as I swallow it.