The primary complications of diabetes due to damage in small blood vessels include damage to the eyes, kidneys, and nerves.[32] Damage to the eyes, known as diabetic retinopathy, is caused by damage to the blood vessels in the retina of the eye, and can result in gradual vision loss and eventual blindness.[32] Diabetes also increases the risk of having glaucoma, cataracts, and other eye problems. It is recommended that diabetics visit an eye doctor once a year.[33] Damage to the kidneys, known as diabetic nephropathy, can lead to tissue scarring, urine protein loss, and eventually chronic kidney disease, sometimes requiring dialysis or kidney transplantation.[32] Damage to the nerves of the body, known as diabetic neuropathy, is the most common complication of diabetes.[32] The symptoms can include numbness, tingling, pain, and altered pain sensation, which can lead to damage to the skin. Diabetes-related foot problems (such as diabetic foot ulcers) may occur, and can be difficult to treat, occasionally requiring amputation. Additionally, proximal diabetic neuropathy causes painful muscle atrophy and weakness.
This happens because constantly high levels of sugar in the blood stream can damage the blood vessels of the penis, or the blood vessels supplying the nerves to the penis. When the blood vessels and nerves are damaged, the blood flow to the penis is significantly reduced, resulting in erectile dysfunction. Other causes of erectile dysfunction include smoking, heart disease, high blood pressure and high cholesterol levels.
Diabetes was one of the first diseases described,[110] with an Egyptian manuscript from c. 1500 BCE mentioning "too great emptying of the urine."[111] The Ebers papyrus includes a recommendation for a drink to take in such cases.[112] The first described cases are believed to have been type 1 diabetes.[111] Indian physicians around the same time identified the disease and classified it as madhumeha or "honey urine", noting the urine would attract ants.[111][112]
No longer is it satisfactory to provide patients who have diabetes with brief instructions and a few pamphlets and expect them to manage their disease adequately. Instead, education of these patients should be an active and concerted effort involving the physician, nutritionist, diabetes educator, and other health professionals. Moreover, diabetes education needs to be a lifetime exercise; believing that it can be accomplished in 1 or 2 encounters is misguided.
It may not be necessary to see an endocrinologist for diabetes care and management. However, those with type 1 diabetes mostly see an endocrinologist, particularly when they are initially diagnosed with the disease. People with type 2 diabetes also see an endocrinologist if they develop severe complications or if they have a difficulty in controlling their diabetes. 
Vascular diseases that prevent blood flow to the small blood vessels are common if you have diabetes. Nerve damage may also occur with longstanding diabetes. Since restricted blood flow and nerve damage can affect the feet in particular, you should make regular visits to a podiatrist. With diabetes, you may also have a reduced ability to heal blisters and cuts, even minor ones. A podiatrist can monitor your feet for any serious infections that could lead to gangrene and amputation. These visits do not take the place of daily foot checks you do yourself.
Diabetes can also be a finding in more severe mitochondrial disorders such as Kearns-Sayre syndrome and mitochondrial encephalomyopathy, lactic acidosis, and strokelike episode (MELAS). Mitochondrial forms of diabetes mellitus should be considered when diabetes occurs in conjunction with hearing loss, myopathy, seizure disorder, strokelike episodes, retinitis pigmentosa, external ophthalmoplegia, or cataracts. These findings are of particular significance if there is evidence of maternal inheritance.
Several other signs and symptoms can mark the onset of diabetes although they are not specific to the disease. In addition to the known ones above, they include blurred vision, headache, fatigue, slow healing of cuts, and itchy skin. Prolonged high blood glucose can cause glucose absorption in the lens of the eye, which leads to changes in its shape, resulting in vision changes. Long-term vision loss can also be caused by diabetic retinopathy. A number of skin rashes that can occur in diabetes are collectively known as diabetic dermadromes.[24]
^ Boussageon R, Bejan-Angoulvant T, Saadatian-Elahi M, Lafont S, Bergeonneau C, Kassaï B, Erpeldinger S, Wright JM, Gueyffier F, Cornu C (July 2011). "Effect of intensive glucose lowering treatment on all cause mortality, cardiovascular death, and microvascular events in type 2 diabetes: meta-analysis of randomised controlled trials". BMJ. 343: d4169. doi:10.1136/bmj.d4169. PMC 3144314. PMID 21791495.
A second oral agent of another class or insulin may be added if metformin is not sufficient after three months.[80] Other classes of medications include: sulfonylureas, thiazolidinediones, dipeptidyl peptidase-4 inhibitors, SGLT2 inhibitors, and glucagon-like peptide-1 analogs.[80] As of 2015 there was no significant difference between these agents.[80] A 2018 review found that SGLT2 inhibitors may be better than glucagon-like peptide-1 analogs or dipeptidyl peptidase-4 inhibitors.[96]

Gestational diabetes mellitus (GDM) resembles type 2 diabetes in several respects, involving a combination of relatively inadequate insulin secretion and responsiveness. It occurs in about 2–10% of all pregnancies and may improve or disappear after delivery.[52] However, after pregnancy approximately 5–10% of women with GDM are found to have DM, most commonly type 2.[52] GDM is fully treatable, but requires careful medical supervision throughout the pregnancy. Management may include dietary changes, blood glucose monitoring, and in some cases, insulin may be required[53]