What it's normally used for
Complex vitamins are vitamins that help your body convert calories into energy. They are also important for vision, normal appetite, and healthy hair, skin, and nails. They also play a role in the creation of red blood cells and help keep the nervous system running. Vitamin B100 complex supplements contain most of the B vitamins in doses of 100 milligrams, except for a few of them that you need in way smaller doses. The 100-milligram dosage is much higher than the recommended daily value, though, because B vitamins are not stored in the body's fat tissues like some vitamins are, B-vitamin toxicity is usually not an issue.
Because B-complex vitamins help convert your food into usable energy, they can also be effective in increasing energy levels.
What it does for Lucid Dreaming
Not being able to remember your dreams can be a hint of B-6 deficiency. B-6 can also help in converting the amino acid tryptophan into serotonin, which wakes up the brain -- especially during Rapid Eye Movement, which is when you dream and have the vivid dreams.
My own results
I take B Maxi or B 100 Complex after six hours of sleep and I remember more of the dream, where it seems like it's a longer dream.