Medical marijuana and CBD dosage is a contentious issue because there are no official dosage guidelines yet. That said, most research indicates therapeutic doses for different disorders and health conditions, and according to a literature review, the majority of these have favorable outcomes. 
We did the digging for you, so read on to discover what to look out for when buying CBD oil for any condition—and also a number of suggested CBD dosages for three different conditions.
Note, though, that no chronic medication should be replaced with CBD or medicinal marijuana without the recommendation and/or knowledge of a qualified physician.
It is also important to know that the ingestion method, dosage, and benefits gained from CBD oil may vary from one person to the next. These are all influenced by factors such as:
What's more, your body changes over time, and your changing chemistry may also influence the action of cannabidiol. There are few to no standardized guidelines in place yet.
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Medical marijuana and its derivatives are not regulated yet, which means that there are many below-par CBD oils and tinctures out there that will do absolutely nothing for you. Or worse—they could poison you.
Also, you need to be able to control your CBD dosage. In fact, following the suggested guidelines in this article will be meaningless unless you are using a superior oil or tincture that indicates exactly how much CBD you're taking. Only then can you be relatively sure of good—if not excellent—outcomes using CBD.
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A good oil or tincture has a number of identifying qualities, and these will normally be clearly stated on the label or in the selling company's marketing material. When you buy, ask yourself the following questions:
Some plants, including hemp, are known to decontaminate soil by pulling toxins out of the soil in a process called phytoremediation. It is sometimes cultivated for this purpose alone, but you don't want your medicine to be made from toxin-laced Cannabis Sativa L. plants. Make sure your supplier is extracting oil from organically cultivated hemp grown in low-pollution areas. 
Heat most often destroys nutrients, and the same goes for the cannabinoids and other healthy compounds in hemp. A carbon dioxide or CO2 extraction method uses solvents that don't leave a residue, and that keeps the hemp plant compounds intact. It's also kinder to the environment than many other methods.
If so, stay clear. CBD works best together with other cannabis compounds such as terpenes and other cannabinoids. It's called the "entourage effect" and makes a huge difference in treatment outcomes. These days, hemp is cultivated to be CBD-dominant, so a whole-plant extract will give you a product that won't cause the slightly infamous “high” marijuana is known for.
Be wary of products that state a percentage of CBD in the oil instead of stating how many milligrams of CBD you get per dosage. CBD oil dosage can be managed much better this way, and a higher percentage of sub-quality CBD oil won't be as effective as a high-quality, low-percentage CBD.
OK, so if you're sure you're sitting with an excellent quality CBD oil, let's look at the doses used in research with favorable outcomes.
Again, these guidelines are not formal recommendations and should not be viewed as such. CBD oil is so far considered safe for human consumption, even in very high doses, but it is up to you to consult with your physician (especially when considering using high-dose CBD oil) and to experiment to find your personal "sweet spot" regarding CBD oil dosages. 
Few things can be more debilitating than chronic pain, and for this, a small but well-designed study has good news.
In over 100 cancer patients who found opioids no longer effective against their pain, a CBD-THC extract showed 30% greater pain relief compared to placebo. It was delivered in an oromucosal spray that administered 2.7 mg THC and 2.5 mg CBD per spray. Patients were allowed to regulate their intake. After a titration period of one week, the mean number of sprays was almost nine per patient per day. That means the patients took approximately 18 mg of THC and CBD per day to effectively manage their symptoms.
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Note: Especially the THC dosages are indicated for very severe and chronic pain, for which you would probably need to be under medical supervision. Consult with your prescribing doctor for guidelines regarding side effects and drug interactions. THC and CBD are used together for the treatment of pain, as they seem to complement each other. 
Another small clinical study (meaning it involved human subjects) showed that "...acute administration of CBD reduces resting BP [blood pressure] and the BP increase to stress in humans, associated with increased HR [heart rate]." In this case, 40 mg of CBD dropped the subjects' blood pressure not only when they were resting, but also when they were subjected to certain stressors. The CBD dosage increased heart rate but did not interfere with cardiac functioning. 
It is highly inadvisable to replace your blood pressure medication with CBD oil or any other remedy without your physician's knowledge and guidance.
Quality clinical research is unfortunately still lacking, but the available data, including anecdotal, is very positive. CBD for anxiety and social anxiety disorder (SAD) has been tested in 24 SAD patients. A CBD dose of 60 mg proved more effective than placebo in ameliorating anxiety and related symptoms.
In another study, 40 mg of CBD significantly reduced subjective anxiety as measured by rating scales. The reviewers concluded that "...the results from laboratory animals, healthy volunteers, and patients with anxiety disorders support the proposition of CBD as a new drug with anxiolytic properties." 
As previously mentioned, CBD dosage is still not standardized for different indications, and more clinically relevant research is needed. However, this shouldn't stop you from experimenting on your own, as thousands across the world can attest to its efficacy.