Lisbon, July 23, 2025 (Lusa) - The Portuguese medicines regulator, Infarmed, warned on Wednesday that intense heat can affect the safety and efficacy of medicines and that some, such as diuretics or antidepressants, can compromise the body’s thermal regulation, especially in the elderly, chronically ill, obese, children and bedridden patients.
To avoid this situation, the National Authority for Medicines and Health Products (Infarmed) has made available on its website the document “Medicines and heat”, which answers frequently asked questions and provides useful advice and guidance on maintaining the effectiveness of medicines.
Infarmed stresses that “exposure to high temperatures can compromise the safety and efficacy of medicines”, and that drugs such as diuretics, antidepressants, antihypertensives and antipsychotics can interfere with the body’s thermal regulation mechanisms.
“This situation is particularly relevant in the elderly, the chronically ill, obese people, children and bedridden people, who have greater difficulty in adapting to the heat,” it stresses.
The head of Infarmed’s Drug Risk Management Directorate (DGRM), Márcia Silva, explains that “in most cases, medicines do not in themselves represent a risk factor, especially when used correctly in accordance with the doctor’s or pharmacist’s instructions”.
However, she warns that "there are numerous risk factors related to health that interfere with the body’s ability to regulate temperature and consequently reduce its ability to withstand heat, and these must be taken into account".
According to Infarmed, medicines should be stored and transported in accordance with the instructions on the package leaflet, as heat can alter their properties.
“Medicines that need to be refrigerated (between 2º C and 8º C) should be transported in refrigerated insulated bags, without being frozen. The rest should also be protected from high temperatures,” it recommends.
The medicines authority advises patients, in the event of a heatwave, not to interrupt their treatment without medical advice, because this decision “can lead to serious complications linked either to the sudden interruption of medication or to the effects of the untreated disease”.
It also recommends that those taking medication should not consume alcoholic beverages, as these aggravate dehydration, and "not to take any medication without the advice of a doctor or pharmacist, even those that do not require a prescription".
Portugal’s national meteorological institute (IPMA) is forecasting a rise in temperatures from Thursday, and especially from Friday, with maximum temperatures reaching above-average figures for the time of year, “beginning to contribute to a heatwave until at least the 30th”.
“A significant rise in air temperature is expected from Thursday 24th, with maximum temperatures above 30 °C across most of the mainland, reaching 40 °C in some places, particularly in the interior of the southern region and the Tagus valley”, according to a statement published on its website.
According to the national meteorological institute, the minimum temperature is expected to exceed 20 °C in some inland areas, particularly in the south, the Tagus valley and Beira Baixa.
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