Seriously, I dont listen to studies anymore. ALMOST anything is reasonably safe if done properly and in moderation. Hell they approve medicinces that have a longer list of negative side effects just to cure a headache or cold, than taking some illegal drugs.
Hell the list of these medications are from anything from a cold to how to have a shorter period if you are a girl and they have sides like dizziness, shortness of breath, cramps, nausea, trouble sleeping, vomiting, fainting, numbness, infirtility and possible death etc...
If you do your research and learn how to use certain things and are as safe as possible with them its normally semi-safe. Most cases of death is user error with any substance.
-Legacy