Within a few minutes after inhaling marijuana smoke, a person’s heart rate speeds up, the breathing passages relax and become enlarged, and blood vessels in the eyes expand, making the eyes look bloodshot. The heart rate—normally 70 to 80 beats per minute—may increase by 20 to 50 beats per minute or may even double in some cases. Taking other drugs with marijuana can amplify this effect.
Limited evidence suggests that a person’s risk of heart attack during the first hour after smoking marijuana is nearly five times his or her usual risk.72 This observation could be partly explained by marijuana raising blood pressure (in some cases) and heart rate and reducing the blood’s capacity to carry oxygen.73 Marijuana may also cause orthostatic hypotension (head rush or dizziness on standing up), possibly raising danger from fainting and falls. Tolerance to some cardiovascular effects often develops with repeated exposure.74 These health effects need to be examined more closely, particularly given the increasing use of "medical marijuana" by people with health issues and older adults who may have increased baseline vulnerability due to age-related cardiovascular risk factors (see "Is marijuana safe and effective as medicine?").
A few studies have shown a clear link between marijuana use in adolescence and increased risk for an aggressive form of testicular cancer (nonseminomatous testicular germ cell tumor) that predominantly strikes young adult males.75,76 The early onset of testicular cancers compared to lung and most other cancers indicates that, whatever the nature of marijuana’s contribution, it may accumulate over just a few years of use.
Studies have shown that in rare cases, chronic use of marijuana can lead to Cannabinoid Hyperemesis Syndrome—a condition marked by recurrent bouts of severe nausea, vomiting, and dehydration. This syndrome has been found to occur in persons under 50 years of age and with a long history of marijuana use. Cannabinoid Hyperemesis Syndrome can lead sufferers to make frequent trips to the emergency room, but may be resolved when a person stops using marijuana.77