There is a reason those who use cannabis for its medicinal value prefer edibles as their method of consumption, versus smoking, which may get into the body quicker, but the effects are shorter in length, and not as strong. The reason for this is because of the way it is absorbed and metabolized (known as pharmacokinetics), and it also depends on the way in which people use it. Meaning, that by smoking, you are able to control the dose easier than consuming the cannabis in an edible-form, and while most people pretty much immediately know when they've hit the 'limit' or the amount they feel comfortable with when smoking, it is a lot harder to know how to dose with edibles.
Mitch Earleywine, the author of Understanding Marijuana, and professor of psychology at the State University of New York in Albany, explains it in a more scientific way:
Smoked or vaporized cannabis, he states, bypasses the liver and does not create the same 11-hydroxy-THC. This doesn't mean either way is more intoxicating, but it is just a different method of delivery, one with a quicker outcome (via smoking) felt almost immediately, and the other can take up to about an hour, and stay in the system for several hours.
"The key difference is in how it’s metabolized", says Dr. Mark A. Ware, an associate professor of family health at McGill University in Montreal. “Anything going through the stomach goes through the liver first,” before it gets into the blood, he explains, a process called first-pass metabolism. Cannabis absorbed through the lungs goes straight to the brain, but is only metabolized by the liver on the second pass. When the liver metabolizes delta-9 THC to 11-hydroxy THC, users feel the combined effect of the two.
This is why people using cannabis medicinally often prefer taking cannabis in an edible-form because the effects are longer-lasting and they don’t have to consume as often to treat their chronic pain or condition.
Predicting the effects of an oral dose is not easy, however, as herbal drugs are difficult to standardize, and the wide varying responses to the same dose is on reason why the medical use of cannabis, common in the late 19th century, had largely faded by the time the U.S. government enacted prohibitive laws in 1937.
Despite those variations, Ware says, once the patients he’s observed have found a dose that works, they tend to stay with that dose—but they must go through the same trial-and-error process when they get a different batch of cannabis. He recommends “the lowest dose possible to achieve therapeutic effects.”