NHSL Medicines Guidance
The use of vitamins as general “pick-me-ups” is of unproven value and, in the case of preparations containing vitamin A or D, may be harmful if the prescribed dose is exceeded.
Mega-vitamin therapy with water-soluble vitamins, such as ascorbic acid and pyridoxine, is unscientific and can be harmful.
For further information see BNF: Treatment summary: Vitamins.