I was wondering if there can be side effects to abruptly stopping b12 and vitamin d vitamins?

No! None: Only sedatives and or tranquilizers have withdrawal symptoms. Vitamins do not have any such problem.

Vitamin B12, and D: Vitamins are essential for your health, growth and functioning Suddenly cutting vitamins from your diet would strain your physical and emotional well-being If your Physician advised you about Balanced Diet with all Vitamins including Vitamin B12 and Vitamin D, do not stop taking Vitamins You can get all of the vitamins you need by eating a well-balanced diet See a Nutritionist.

Vitamins: There should not be any significant side effects by stopping any of the supplemental vitamins, including your B-12 and Vitamin D.

No: Both Vit D & B12 are stored in the body (of interest, B12 is the only B vi we can store) so stopping will have no immediate effect. Those with good digestion who eat animal-derived foods usually get adequate B12 from diet; vegans & those on acid-blocking drugs should supplement. One can get adequate D from sun exposure in spring & summer but everyone should take 5-8000 iu of D in fall & winter.

Not likely: There should be no immediate ill effects for you to come off of these vitamins.