to go on to smoke cigarettes. Their part in tobacco harm reduction is unclear, while another review found they appear to have the potential to lower tobacco-related death and disease. Regulated US Food and Drug Administration nicotine replacement products may be safer than e-cigarettes, but e-cigarettes are generally seen as safer than combusted tobacco products. It is estimated their safety risk to users is similar to that of smokeless tobacco. The long-term effects of e-cigarette use are unknown. The risk from serious adverse events was reported in 2016 to be low. Less serious adverse effects include abdominal pain, headache, blurry vision, throat and mouth irritation, vomiting, nausea, and coughing. Nicotine itself is associated with some health harms. In 2019 and 2020, an outbreak of severe lung illness throughout the US has been linked to the use of contaminated black market THC vape cartridges. Other drug Vaporizers can be used to inhale other recreational drugs as well. A wide variety can be consumed this way, either dissolved in e-liquid or vaporized directly. The use of e-cigarettes to inhale the psychedelic drug DMT has been reported. Medical vaporizers Studies have shown that vaporizing cannabis exposes the user to lower levels of harmful substances than smoking cannabis. These findings are important for it is estimated that 10–20% of patients with chronic pain, multiple sclerosis, epilepsy, and HIV/AIDS have admitted to smoking cannabis for therapeutic purposes. For patients, a study found that smoking cannabis sativa reduced daily pain by 34%, a statistically significant amount. In a study published in the Journal of Psychopharmacology in May 2008, it was stated that vaporizers were a "suitable method for the administration of THC". A 2007 study by the University of California, San Francisco, published in the Journal of the American Academy of Neurology, found that "there was virtually no exposure to harmful combustion products using the vaporizing device". A 2006 study performed by researchers at Leiden University found that vaporizers were "safe and effective cannabinoid delivery system(s)". The study stated that the amount of THC delivered by vaporizers were equivalent to the amount delivered by smoking. Because of those studies and other studies, vaporizers are considered medically sound devices for delivering THC. Efficiency The proposed factors affecting output include: Temperature Specimen density Weight, content of water and essential oils Consistency of material in the filling chamber Storage time of the vapor Inhalation method (breathing technique) Not all