What does extreme heat do to medications? I found out while we were sweating out the recent heat wave in a lake cabin in New Hampshire and my 10-year-old son’s allergies kicked up.

I gave him a dose of over-the-counter medicine that usually brings quick relief. But this time the drug had no effect. The same thing happened the next day, and the next.|

When I returned home, I asked a pharmacist about it. Was my son becoming immune to this particular medicine? Were his allergies getting worse?

The pharmacist asked where I had stored his pills as the temperatures soared. On the bathroom shelf in the cabin, I said. And on the sweltering six-hour drive to the lake? The medicine was in my suitcase in the trunk of the car.

And that’s when I learned this: No drug should be exposed to temperatures higher than 86 degrees. Some days the bathroom at our vacation house and certainly the trunk of the car were well above that mark.

Extreme temperatures can have a big effect on both prescription and over-the-counter drugs.

Pharmaceutical manufacturers recommend most of their products be stored at a controlled room temperature of 68 to 77 degrees, said Skye McKennon, clinical assistant professor at the University of Washington School of Pharmacy. In truth, that is the range in which manufacturers guarantee product integrity. Anywhere from 58 to 86 degrees is still fine, she said.

“During heat waves and cold spells, storage locations can go above or below those ranges, causing medicines to physically change, lose potency or even threaten your health,” Dr. McKennon said.

For patients with such chronic illnesses as diabetes or heart disease, a damaged dose of a crucial medicine, like insulin or nitroglycerin, can be life-threatening. But even common medicines can break down with potentially harmful effects, and you can’t always tell by looking at the pill or liquid that a problem has occurred, said Janet Engle, a pharmacist and past president of the American Pharmacists Association.

When some antibiotics decay, they can cause stomach or kidney damage, Dr. McKennon said. Compromised aspirin can cause more than the usual stomach upset. Hydrocortisone cream can separate and become useless in the heat.

Any type of diagnostic test strip, like those used to test for blood sugar levels, pregnancy or ovulation, is extremely sensitive to humidity. If moisture sticks to the strips, it will dilute the test liquid and possible give a false reading.

Thyroid, birth control and other medicines that contain hormones are especially susceptible to temperature changes. These are often protein-based, and when protein gets hot it changes properties. “Think of an egg,” Dr. McKennon said. “When it gets hot, it cooks.”

Special care should also be taken with insulin, seizure medicines and anticoagulants, Dr. McKennon said. “Small changes in doses in some medicines like these can make a big difference to your health,” she said.

Although it is hard to imagine freezing temperatures in the midst of August, keep in mind that cold can be a culprit, too. Drugs like insulin can lose their effectiveness if they freeze. The same goes for any so-called suspended medication that has to be shaken before use.

To make sure your medicines stay safe, here’s some advice culled from pharmacists and other experts.

A COOL, DRY PLACE Despite the name, the medicine cabinet is often the worst place to store drugs because of the frequent high humidity in the bathroom. (Moisture is a particular menace for quick-dissolve tablets, the type my son was taking.)

Instead, save that space for bandages and toothpaste. Keep medicines in a cool, dry place, like a hallway linen closet, bedroom closet or even a kitchen cabinet away from the stove. If children or animals can get into these spaces, consider a higher shelf or lockbox.

SPECIAL PACKAGING Don’t be lulled by expensive special packages designed to “protect” drugs, like a bubble or foil pack. There is no evidence that these packages protect medicine any better than a standard pill bottle, Dr. McKennon said.

That said, never take medicine out of the original packaging where it may be more exposed to the elements. One exception: Elderly or seriously ill patients often need day-by-day pill boxes to help keep their dosages accurate. These should be stored in a cool, dry place.

A special note about insulin: It can easily degrade if it is frozen or too hot, said Dr. Vivian Fonseca, a physician and president-elect of the American Diabetes Association. Unopened bottles of insulin are best kept in the refrigerator. Open bottles, however, can be kept at room temperature, which also makes injections more comfortable. ~nytimes.com~