Newly updated guidelines reaffirm that metformin is the first-line drug for people with type 2 diabetes, and that several other medications -- including newer ones -- can be added if needed.

The recommendations come from the American College of Physicians (ACP). The American Academy of Family Physicians endorsed the new guidelines. The ACP updated the guidelines because of new research into diabetes drugs, and the U.S. Food and Drug Administration approval of new diabetes drugs.

"Metformin, unless contraindicated, is an effective treatment strategy because it has better effectiveness, is associated with fewer adverse effects, and is cheaper than most other oral medications," ACP president Dr. Nitin Damle said in a college news release.

"The escalating rates of obesity in the U.S. are increasing the incidence and prevalence of diabetes substantially. Metformin has the added benefit of being associated with weight loss," Damle said.

The ACP recommends that if a patient needs to take a second drug by mouth to lower blood sugar levels, physicians should look at adding a sulfonylurea, thiazolidinedione, SGLT-2 inhibitor, or a DPP-4 inhibitor.

Examples of sulfonylurea drugs include glyburide (Diabeta, Glucovance, Micronase), glimepiride, glipizide (Glucotrol) and tolbutamide. Thiazolidinedione drugs include pioglitazone (Actos) and rosiglitazone (Avandia).

SGLT-2 inhibitors include canagliflozin (Invokana), empagliflozin (Jardiance) and dapagliflozin (Farxiga). DPP-4 inhibitors include sitagliptin (Janumet, Januvia) or linagliptin (Jentadueto, Tradjenta). Brand names for metformin include Glumetza, Glucophage, and Fortamet.

"Adding a second medication to metformin may provide additional benefits," Damle said.

"However, the increased cost may not always support the added benefit, particularly for the more expensive, newer medications. ACP recommends that clinicians and patients discuss the benefits, adverse effects, and costs of additional medications," he added.

An estimated 29 million people in the United States have diabetes, according to the U.S. Centers for Disease Control and Prevention.

The guidelines are published in the Jan. 3 issue of the Annals of Internal Medicine.