Drisdol is the form of vitamin D you are likely to get if you receive a prescription for vitamin D from a doctor. It is vitamin D2 -- which is not the form of vitamin D your body produces in response to sun exposure, vitamin D3. Vitamin D2 is made by irradiating fungus and plant matter.
A recent review and meta-analysis compared the efficacy of D2 and D3. It examined 50 randomized controlled trials with a total of 94,000 participants. There proved to be a 6% relative mortality risk reduction when supplementing with vitamin D3, but a 2% relative risk increase when supplementing with vitamin D2
According to the Vitamin D Council:
“You would think a paper that took a look at tens of thousands of subjects and analyzed the efficacy of prescription vitamin D (D2) and over-the-counter vitamin D (D3) would warrant a news story or two. To my knowledge, these papers are the first to paint such a clear picture about the efficacy between D3 and D2. While there may be explanations for D3’s superiority other than improved efficacy, for the time being, these papers send doctors a message: use D3, not D2.”