Is marijuana an effective medicine for any one of these medical conditions?

Question

Has marijuana been shown to be an effective medicine for any one of these medical conditions: pain, glaucoma, cancer, HIV/AIDS, Alzheimer's disease, or multiple sclerosis?

For purposes of this question:

• "effective" means that marijuana works as well as or better than available alternatives and with comparable or fewer negative side effects; or it works nearly as well as available alternatives, but with fewer negative side effects; or it can successfully treat a condition for which there are no alternative treatments.

• "marijuana" means any unpurified parts of cannabis plants (as opposed to purified extracts such as THC).

Following are some examples of claims that marijuana can be used to effectively treat a variety of serious medical conditions:

There is a subpopulation of people suffering from cancer, HIV/AIDS, amyotrophic lateral sclerosis (ALS), chronic pain and other debilitating illnesses for whom existing medications are ineffective or cause dangerous side effects. For many of these patients, medical marijuana can provide a superior treatment alternative.

-- Massachusetts Patient Advocacy Alliance

The evidence is overwhelming that marijuana can relieve certain types of pain, nausea, vomiting and other symptoms caused by such illnesses as multiple sclerosis, cancer and AIDS -- or by the harsh drugs sometimes used to treat them. And it can do so with remarkable safety. Indeed, marijuana is less toxic than many of the drugs that physicians prescribe every day.

-- Dr. Joycelyn Elders, former U.S. Surgeon General

Supporters of medical cannabis argue that cannabis does have several well-documented beneficial effects. Among these are: the amelioration of nausea and vomiting, stimulation of hunger in chemotherapy and AIDS patients, lowered intraocular eye pressure (shown to be effective for treating glaucoma), as well as gastrointestinal illness. Its effectiveness as an analgesic has been suggested—and disputed—as well.

-- Wikipedia article on Medical Marijuana

Answer 1

There are details, with a list of more than 250 references/citations, at Information for Health Care Professionals: Marihuana (marijuana, cannabis) [Health Canada, 2010] (hyperlink).

It talks about the following clinical uses:

4.1 Nausea and vomiting
4.2 Wasting syndrome and loss of appetite in AIDS and cancer patients
4.2.1 To stimulate appetite and produce weight gain in AIDS patients
4.2.2 To stimulate appetite and produce weight gain in cancer patients
4.2.3 Anorexia nervosa
4.3 Multiple sclerosis, amyotrophic lateral sclerosis, spinal cord injury
4.3.1 Multiple sclerosis
4.3.2 Amyotrophic lateral sclerosis
4.3.3 Spinal cord injury
4.4 Epilepsy
4.5 Pain
4.5.1 Cancer pain
4.5.2 Non-cancer pain
4.5.2.1 Postoperative pain
4.5.2.2 Neuropathic pain
4.5.2.3 Rheumatoid arthritis
4.5.2.4 Headache
4.5.2.5 Fibromyalgia
4.6 Other diseases and symptoms
4.6.1 Movement disorders
4.6.1.1 Dystonia
4.6.1.2 Huntington's disease
4.6.1.3 Parkinson's disease
4.6.1.4 Tourette's syndrome
4.6.2 Glaucoma
4.6.3 Asthma
4.6.4 Hypertension
4.6.5 Psychiatric disorders
4.6.6 Alzheimer's disease
4.6.7 Inflammation
4.6.7.1 Inflammatory bowel disease
4.6.7.2 Inflammatory skin diseases
4.6.8 Bladder dysfunction
4.6.9 Anti-neoplastic properties

I can't quote it all, but to pick one sentence:

While cannabinoids present clear advantages over placebo in the control of CINV, the evidence from randomized trials shows cannabinoids to be clinically only slightly better than conventional dopamine D2-receptor antagonist anti-emetics (114,115).

So the answer is yes to the first two parts of our question:

1. It is comparably effective
2. For cancer (e.g. for controlling chemotherapy-induced nausea)

The third part of your question was, "marijuana means any unpurified parts of cannabis plants (as opposed to purified extracts such as THC)".

It says things like,

The ability of marihuana to stimulate appetite and food intake has been applied to clinical situations where weight gain is deemed beneficial such as in HIV-associated muscle wasting and weight loss. One study showed that experienced HIV+ marihuana smokers with clinically significant muscle mass loss benefited from both dronabinol (4-8 times the standard 2.5 mg b.i.d dose or 10-20 mg daily) and smoked marihuana (3 puffs at 40 sec intervals, 1.3-3.9% THC). Both drugs produced substantial and comparable increases in food intake and body weight, as well as improvements in mood and sleep (130,131). The marihuana-associated increase in body weight appeared to result from an increase in body fat rather than lean muscle mass (132,133).

It goes on to say,

Oral synthetic THC, dronabinol, administered as capsules (Marinol®) is an approved indication in Canada for AIDS-related anorexia associated with weight loss.

They previously said that smoked marijuana is effective.

I expect that synthetics (purified extracts) are prescribed, not because they're more effective but because they have fewer adverse side-effects, for example smoking tar etc.