Re: Metformin slows growth of tumors lacking p53

For liver and kidney and heart problems, it is fine if you do not already have those. 

Metformin is not recommended for people who have a history of kidney or liver disease, or a history of congestive heart failure. People with a history of alcohol abuse should also avoid taking the drug, as serious lactic acidosis can develop in these individuals.

http://curezone.com/blogs/m.asp?f=1184&i=141

The only side effect I have witnessed in about 10% of my patients is stomach upset and diarrhea. I've found, however, that almost everyone can build up a tolerance to it. I suggest that my patients start with a low dose, as little as one, or even a half tablet per day for a week or two, and then gradually increase the dose as they develop a tolerance. There is a theoretical problem of lactic acidosis in patients with impaired kidney function, but in practice, I have never seen this, despite monitoring thousands of patients on Metformin. Nevertheless, I believe that anyone with impaired kidney function should take Metformin only under the care of a physician, and should have their blood levels of lactic acid checked periodically.

Metformin has been shown to impair the absorption of vitamin B12, so it is probably prudent to make sure that you’re taking plenty of B12. I don’t have to tell my patients that, of course, as they’re usually already taking plenty of vitamins. Metformin has also been shown to raise homocysteine, so extra folic acid and Vitamin B6 should also be taken. If homocysteine levels are elevated, I recommend adding Anhydrous Betain (Trimethylglycine) in a dose of about 6-9 grams per day. If a patient is diabetic, or a starch junkie, the starch blocker Acarbose (Glucobay) can also be used. If the patient is a diabetic, I would add Actos or Avandia to the Metformin. These are also insulin receptor sensitizing drugs which can enhance the glucose-lowering efficacy of Metformin by up to about 30%.

http://www.antiaging-magazine.com/interviews/interview_1.html