July 25 (Reuters) - The world just experienced the

hottest day on record and prolonged heat waves have become more

common due to climate change, conditions that can alter

medications and their effects on patients taking them.

Here is what you need to know about medicines in hot

weather:

HOW DOES HEAT ALTER THE EFFECTS AND QUALITY OF MEDICINES?

Medications for common conditions can increase patients'

sensitivity to heat by impairing the body's response to high

temperatures, including the ability to sweat and the rate of

blood flow.

Heat waves also increase the risk of deterioration for

nearly all medications, whether capsules, sprays, tablets,

syrups, or some other form, if they are not kept within a

certain temperature range.

The heat-related effects of medications can vary based on

individual health status, dosage and environmental conditions.

Patients should consult their physicians about potentially

adjusting doses or scheduling in hot weather, and they should

keep cool by staying hydrated, carrying fans, and seeking shade

or air conditioning, experts say.

WHAT MEDICATIONS INCREASE SENSITIVITY TO HEAT?

- Blood pressure and heart failure medications: Angiotensin

converting enzyme (ACE) inhibitors suppress thirst, making it

harder to know when to drink more water and increasing the risk

of dehydration. Calcium channel blockers can cause mineral

imbalances, making it harder for the body to regulate its

temperature, while beta blockers can make it harder to sweat and

keep the body cool. Diuretics, or water pills, can also cause

dehydration and mineral imbalances.

- Allergy medications: Some over-the-counter antihistamines

reduce sweating and can impair temperature regulation.

- Psychiatric medications: Certain antipsychotic

medications limit patients' ability to sweat. Some

antidepressants have the opposite effect, increasing sweating

and repressing thirst. Stimulants such as amphetamines and other

drugs used to treat attention deficit hyperactivity disorder may

interact with the central nervous system to raise body

temperature.

- Thyroid medications: Thyroid hormone pills also can raise

body temperature, impair temperature regulation and cause

excessive sweating.

WHAT IS A SAFE TEMPERATURE RANGE FOR STORING MEDICATIONS?

Extreme heat (and extreme cold) can significantly alter the

effectiveness of prescription and over-the-counter drugs.

Some medications can tolerate temperatures up to 86 degrees

Fahrenheit (30 Celsius), but in general they should be stored at

59-77 F (15-25 C) in a cool, dry place, away from sunlight.

Temperature storage guidelines for specific drugs can be found

on manufacturers' websites.

It's hard to predict the extent to which a medication will

degrade in extreme temperatures because each drug is different,

said Amy Bachyrycz, a pharmacy faculty member at the University

of New Mexico in Albuquerque.

In general, medicines should not be left in hot cars or for

hours in hot mail boxes if they are mail-ordered medications.

A spokesperson for CVS Health's ( CVS ) Caremark pharmacy

benefits unit said the company's electronic shipping system

takes weather data into account to determine appropriate

packaging materials for each shipment.

An Amazon.com Pharmacy spokesperson said the

company employs strict storage and delivery safety measures to

protect medications from extreme temperatures throughout the

shipping process.