"While many drugs clearly fall into the category of either stimulant, depressant, or hallucinogen, cannabis exhibits a mix of all properties, perhaps leaning the most towards hallucinogenic or psychedelic properties, though with other effects quite pronounced as well. Though THC is typically considered the primary active component of the cannabis plant, various scientific studies have suggested that certain other cannabinoids like CBD may also play a significant role in its psychoactive effects." Wiki

Marijuana is considered mildly hallucinogenic due to it's affects on short term memory. Depending on the strain, marijuana can be either a stimulant or depressant. Sativa strains are stimulants, while Indica strains, because of having CB, another psychoactive cannabinoid which has a sedative effect, are depressants.

Using marijuana for medical purposes means controlled dosages. Likely less then a recreational user might expect. It will vary but dosages usally average 2 grams a day depending on how it is taken. Use will also be determined based on effect. It varies from person to person. I know people who just fall asleep immediately while others actually get energized. I cam experience either. Sometimes it seems to heighten my creativity and sensory responses and other times it just relaxes me so I can sleep. Depends on the strain, how much I use and for how long I use it.

Controlling use for medical purposes is generally not intended to "over dose" a patient no more then any other medication. The proper dosage to minimize a symptom is the intention. At the proper dosage it would likely be considered a pretty mild 'stone' if any real noticable stone at all to a regular recreational user.

People can misuse marijuana just like they can any medication but the system is pretty controlled and high dosages would need to be justified.