The internet has always been a place for people to connect with drug sellers. “The Dr. Oz Show” discovered that some of the drugs in highest demand aren’t used recreationally; they are ones people need to stay alive.

The show recently conducted an undercover investigation into the black market for insulin, used by people with Type 1 and Type 2 diabetes to control their glucose levels and to prevent life-threatening reactions such as ketoacidosis and diabetes-related complications such as retinopathy and neuropathy.

The show found that insulin prices have skyrocketed — more than tripling in the past decade, according to an analysis from IBM Watson Health. Globally, three companies dominate the insulin market, and all of them have raised their prices dramatically. The original price of Humalog, for example, in 1996 was $21 a vial; it is now $275.

Why have prices gone up so steeply? Experts say it’s a result of inadequately designed insurance coverage in both private insurance and Medicare, and alleged price fixing by pharmaceutical companies. Another source of trouble: the rebate system. It provides incentives for middlemen — pharmacy benefit managers, such as CVS, Express Scripts and UnitedHealth’s Optum — to accept high-priced drugs and not pass available savings on to consumers.

This is forcing many people to reduce their lifesaving use of insulin. A study in JAMA Internal Medicine found that 1 in 4 diabetic patients reported rationing insulin because of the cost. Interestingly, very few of the patients surveyed were uninsured, but their out-of-pocket costs were still prohibitively high and, report the researchers, so were their blood sugar levels. No wonder many people are now buying insulin from strangers on the internet.

To see how that happens, “The Dr. Oz Show” sent an investigative correspondent armed with a hidden camera out to buy some black market insulin. She contacted a seller she found online and was able to buy a box of insulin pens, which usually costs $400, for $125.

Such deals may seem smart financially, but buying your insulin on the sly can trigger health problems, even death. One of the other sellers the undercover correspondent met said he kept the insulin in a freezer, a move that erases the drug’s effectiveness in controlling blood sugar levels.

Remember, the way you store insulin matters, and the type you buy matters, too. Not all insulins work the same way, and some may not offer the timing or glucose control that you need.

There are insulins that are rapid-acting, short-acting, intermediate-acting, long-acting and ultra-long-acting. And, says ConsumerMedsafety.org, their similar- sounding names and numbers are easily mixed up. Consider these: Humalog, Humalog 75/25, Humulin Regular, Humulin NPH, Humulin 60/30, Humulin 70/30, Novolog, Novolog 70/30 and Novolin 70/30, Novolin Regular and Novolin NPH.

They cannot be substituted for one another without careful consultation with your doctor and a redesign of your insulin administration plan.

So resist the temptation to buy under shady circumstances. If you or a loved one cannot afford insulin:

>> The American Diabetes Association suggests you ask your doctor if you can use older human insulins in place of more costly newer analogues, and opt for insulin in vials instead of the more costly pens.

>> The ADA also suggests you “talk to your doctor to ensure that your prescription reflects your medication usage each month to avoid multiple monthly copays.”

>> The ADA lists organizations and companies that provide info on pharmaceutical discount programs and databases such as NeedyMeds.org. Go to tinyurl.com/htbzqvy.

>> We also think that if you have Type 2 diabetes, you should ask your doc about other glucose-control medications that may offer an alternative to insulin. One example: GLP-1 receptor agonists, such as Trulicity, that stimulate insulin production while suppressing the liver’s glucose output.

>> There are also a number of apps, including one from Sharecare.com, that use GPS so you can compare insulin prices at pharmacies in your area.