There is mixed research on whether vitamin D3 makes you sleepy. Some studies suggest that it can cause drowsiness in some people, while other studies find no link between the two. More research is needed to determine if there is a definitive relationship between the two. If you are taking vitamin D3 and feel sleepy, it may be best to speak with your doctor to see if there could be another underlying cause. Source: https://www.xplace.com/u/fioterqukon1986 https://uk.askmefast.com/categorydetail.php?cmd=ulist&userid=473686