Will Mucinex D cause sleeplessness?

Yes, take early in the morning and 6 hrs before bed helped me.

Yes, one of the side effects is insomnia.

Keep taking Mucinex D and talk to your doctor if you have any of these less serious Mucinex D side effects:

dizziness or headache;
feeling excited or restless;
*sleep problems (insomnia);*
nausea, vomiting, or stomach upset;
mild loss of appetite;
warmth, tingling, or redness under your skin; or
skin rash or itching.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect. You may report side effects to FDA at 1-800-FDA-1088.

https://www.drugs.com/mucinex-d.html

Take care,