Will diltiazem cause sleep disorder?

Yes, I found in literature while I am sleepless since a week. I couldn't find if there is an explanation for. Betablockers are known to deplete brain of melatonin. Taking 1-3 mg with 1 hour before bed helped me ith. Unfortunately I had another very little known side effect of Metoprolol watery diarrhea in huge amount for a week which took me to emergency room. The problem is they are under reported in ambulatory. Therefore, there are few studies about causes on specific side effects.

I have been a sleep tech for >17yrs and have never had a Patient relay this as a "side effect" of Diltiazem, if anything quite the opposite with c/o excessive lethargy being very common. However, this is not to say that your "reaction" to this medication may well be an "allergic" one an I would definitely consult your prescribing physician. Maintenance insomnia is a very cruel and frustrating thing and maybe this channel blocker may not be the one for you. Good Luck and hope you find a solution soon as well as some restorative sleep.

Undesirable effects of Diltiazem include hypotension, bradycardia, dizziness, flushing.[3] It's quite possible,however, unlikely unless you notice you are experiencing the above symptoms when you awake.
Best regards.

3^ Ramoska, EA; Spiller, HA; Winter, M; Borys, D (1993). "A one-year evaluation of calcium channel blocker overdoses: toxicity and treatment". Annals of emergency medicine 22 (2): 196–200. PMID 8427431.

I checked for possible side effects and sleep disorder is not listed as such.

Even if it is not listed it could still be a potential side effect, I suggest you contact your Dr. and inform him / her about it.

Insomnia can really get to you, I suffer from it so I understand how you must be feeling.

List of possible side effects for future reference:

https://www.drugs.com/sfx/diltiazem-side-effects.html

Take care.