I used to give myself B-12 shots 1000 mcg. in a 1cc diabetic syringe in my deltoid of my arm once a month when I was living in the USA. They won't give me that option in Europe.
This was the cyanocobalamin. Now, I take b-12 sublingual 1000 mcg. 1 under the tongue once a month. There are different vitamin b-12's. The cyanocobalamin b-12 is more synthetic and less "bio-available" than say, the b-12 you would get from red meat, which is more like methylcobalamin. I thought I struck gold when I found out there was methylcobalamin 1000 mcg. sublingual on the market! I hadn't had that much excitement since I bought a new pair of shoes. As far as I know, b-12 will only elevate blood pressure depending on the amount and route of administration. If you inject it intramuscular, you have to do a "register" first- draw back on the syringe to make sure it isn't going directly into a blood vessel. If you do it sublingual, it depends on the amount and frequency. If a person is lacking b-12, they are more likely to notice the "rush" than a person who is sufficient in b-12. Urine is likely to be more bright neon in appearance after taking b-12 if there's a deficiency.
A good magnesium supplement helps dilate arteries and vessels and relax soft muscle tissue and have a calming effect while lowering blood pressure. I use Magnesium Malate 600 mg daily. I stay away from mag. citrates and oxides, they can cause diarrhea are are not absorbed. You can read up on this, it's interesting.