Can Lactaid cause constipation?

Yes, generally the next day if you take “too much” the preceding day.

One of my neighbors has also experienced this.

along with me and several others have used this product and even under the listing of www.drugs.com and other books I have not found where this causes this problem, if it does for you then it may not be the lactaid you could discontinue it then start it again and see what rersults you have best wishes

I checked for possible side effects and constipation is not listed.

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

I suggest you contact your Dr. or Pharmacist to find a solution for your problem.

Take care.