Today I was asked the question whether medical cannabis would ease symptoms of bipolar disorder. I'll come right out and say "pot" almost certainly won't, but there is a strain of marijuana that might be helpful in managing the highs.
I'm not writing from personal experience, however.
Marijuana's best known chemical constituent is tetrahydrocannabinol, also known as THC. This is the chemical that is responsible for the "high" most users of marijuana get from most strains of marijuana. "Higher" isn't exactly a good thing when you're already too high from the manic phase of the disease itself. There is scientific evidence that using marijuana (recreationally, from dealers who don't monitor the chemistry of their product) more than three times a week is generally associated with longer bouts of depression and shorter periods of feeling good.
THC, however, isn't the only chemical in pot. Among 700 or so other known compounds, there is also a major component called CBD, or cannabidiol. This is the chemical that helps users mellow out. It doesn't get you high, and it doesn't get you stoned. It simply helps you relax. CBD might be useful in managing the "high" phases of bipolar disorder. But you'd need a strain of marijuana that is low in THC and high in CBD.
The best known high-CBD strain is Cannatonic. There are others, but you're probably better off working with a provider like Constance Pure Botanical Extracts, within the legal system, because they can help you with the dosage and side effects and whether it's really working for you. Weed you buy on the street is simply not a good idea. Cannabis oil is a better way to get CBD into your system than smoking or vaping, and you need a provider with an analytics lab to make sure you're getting the kind of weed you need.
Medical cannabis you buy legally from a licensed and reputable dispensary will do you a lot more good for managing bipolar disorder--but neither marijuana nor any other medicinal product is a panacea. It's possible that even high-CBD marijuana just isn't what you need. Fortunately, there are many other products that help along with medication management and psychiatric supervision. Bipolar disorder is a tough condition to manage, but it usually can be managed.