Marijuana has a class of drugs, but legally it is considered a Schedule 1 Narcotic Drugs by the DEA. This means that it is defined as having a high potential for abuse and not accepted for medical use. Some countries do not agree with this and have laws on the books legalizing marijuana for medicinal use.
Low-grade marijuana contains 1 to 3 percent of delta-9-tetrahydrocannabinol (THC), which is what is usually sold recreationally. THC is widely recognized as the most active psychoactive agent in marijuana. High-grade marijuana, known as sinsemilla contains 7 to 8 percent THC, and marijuana is between 7 and 20 percent. The most concentrated form of marijuana is hash oils which may contain up to 70% THC!
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How one feels: People's experience with marijuana smoke will vary widely among individuals. Usually one experiences relaxation and mood elevation in a matter of minutes and about half an hour later sedation and drowsiness. The contemplative silence period is often interspersed with excitement.
Learning and memory functions may be affected for a long time even after other effects wear off. It takes a long time for the brain to eliminate marijuana (and its metabolites), so that cognitive function may be affected for more than a day after smoking or ingesting a single dose.
Marijuana does not increase heart rate and places a greater workload on the heart. So there may be interactions with heart or blood pressure medications, but more work needs to be done to explain the specifics.