By "cracking your neck" I mean tilting your head sideways down to the shoulder (and maybe using your hand to pull it further), producing a cracking/popping sound. Many people tell me it's "dangerous". I've heard completely conflicting opinions from different doctors.
Yes (probably if you are young adult).
Chiropractic neck manipulation is known to positively associated with dissection and occlusion of vertebral artery, this is especially true for young adults. 1
What you have asked is cervical self manipulation. Yes there has been cases reported with patients having vertebral artery strokes due to cervical self manipulation.
The first two such cases were reported in October 1991 edition of Neurolgy.
Cook and Sanstead reported Wallenberg syndrome (lateral medullary infarction) in a 33 year old woman. 2
Rothrock et al reported a similiar case of vertebral artery occlusion in a 35 year old man. 3
In February 1991, Johnson et al reported another case in 26 year old male in The Australian Medical Journal. 4
The last paper also made some strong observations that this practice of cervical self manipulation should be strongly discouraged and neck manipulation (self maipulation) should be considered a cause of stroke.
Another observation one can make from all these three cases is that apart from being young, all three went for chiropractic neck manipulation in their past. In the first two cases although it all appears experimental self manipulation gone wrong, in the last case the chiropractor had actually instructed how to self manipulate, making the whole exercise more hazardous.
- Rothwell, D. M., Bondy, S. J., & Williams, J. I. (2001). Chiropractic manipulation and stroke a population-based case-control study. Stroke, 32(5), 1054-1060.
- Cook, J. W., & Sanstead, J. K. (1991). Wallenberg's syndrome following self‐induced manipulation. Neurology, 41(10), 1695-1695.
- Rothrock, J. F., Hesselink, J. R., & Teacher, T. M. (1991). Vertebral artery occlusion and stroke from cervical self‐manipulation. Neurology, 41(10), 1696-1696.
- Johnson, D. W., Whiting, G., & Pender, M. P. (1993). Cervical self-manipulation and stroke. Medical Journal of Australia, 158(4), 290.
Neck manipulation can cause a risk of stroke, but chiropractic neck adjustment is significantly more vigorous than the kind most people give themselves. Whipping your neck around can tear an artery, but simply bending it until you get a satisfying pop is unlikely to do so.
It is certainly possible that there is an enhanced risk of stroke, but it is very unlikely. See the related question about knuckle cracking mentioned by oddthinking for any other effects.
The reason people tell you not to do it, in my personal experience, has more to do with their personal dislike of the noise than any medical information, as there have certainly not been conclusive studies proving that popping of any knuckle is bad for you.